Memory, 2015 Vol. 23, No. 5, 695–713, http://dx.doi.org/10.1080/09658211.2014.921714

Memory impairment among people who are homeless: A systematic review Naomi Ennis1, Sylvain Roy2,3, and Jane Topolovec-Vranic4,5 1

Head Injury Clinic, St. Michael’s Hospital, Toronto, ON, Canada Inner City Family Health Team, Toronto, ON, Canada 3 Psychosocial Rehabilitation Assessment Service, Complex Mental Illness Program, Centre for Addiction and Mental Health (CAMH), Toronto, ON, Canada 4 Trauma and Neurosurgery Program and Li Ka Shing Knowledge Institute, St. Michael’s Hospital, Toronto, ON, Canada 5 Department of Occupational Science and Occupational Therapy, University of Toronto, Toronto, ON, Canada 2

(Received 2 December 2013; accepted 2 May 2014)

Cognitive impairment may interfere with an individual’s ability to function independently in the community and may increase the risk of becoming and remaining homeless. The purpose of this study was to systematically review the literature on memory deficits among people who are homeless in order to gain a better understanding of its nature, causes and prevalence. Studies that measured memory functioning as an outcome among a sample of homeless persons were included. Data on sampling, outcome measures, facet of memory explored and prevalence of memory impairment were extracted from all selected research studies. Included studies were evaluated using a critical appraisal process targetted for reviewing prevalance studies. Eleven studies were included in the review. Verbal memory was the most commonly studied facet of memory. Potential contributing factors to memory deficits among persons who are homeless were explored in seven studies. Memory deficits were common among the samples of homeless persons studied. However, there was a great deal of variation in the methodology and quality of the included studies. Conceptualisations of “homelessness” also differed across studies. There is a need for more controlled research using validated neuropsychological tools to evaluate memory impairment among people who are homeless.

Keywords: Homeless; Memory impairment; Systematic review; Verbal memory; Prevalence.

Homelessness is estimated to affect 100 million people globally (United Nations Comission on Human Rights, 2005) and between 150,000 (Pye, 2005) and 300,000 persons in Canada (Echenberg & Jensen, 2008; Laird, 2007). It poses a significant financial burden on society. For example, there are 1128 emergency and transitional shelters across Canada (Echenberg & Jensen, 2008), and the sum of the 2011 operating budgets for all shelters in Toronto, the country’s

largest city, was estimated to be $60,323,000 (General Manager, 2011). Across all services and jurisdictions, the cost of homelessness to Canadian taxpayers between 1993 and 2004 was estimated at $49.5 billion (Laird, 2007). Homelessness is also associated with multiple adversities to the individual, including infectious (Raoult, Foucault, & Brouqui, 2001) and chronic diseases (Hwang, 2001), mental illness (North, Eyrich, Pollio, & Spitznagel, 2004), increased risk

Address correspondence to: Jane Topolovec-Vranic, Trauma and Neurosurgery Program and Li Ka Shing Knowledge Institute, St. Michael's Hospital, Toronto, ON M5B 1W8, Canada. E-mail: [email protected]

© 2014 Taylor & Francis

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of mortality, substance dependence (Heffron, Skipper, & Lambert, 1997) and cognitive impairments (Burra, Stergiopoulos, & Rourke, 2009). In fact, recent research reveals that up to 80% of homeless individuals demonstrate cognitive impairments such as learning and memory (Burra et al., 2009). Cognitive impairments may interfere with an individual’s ability to function independently in the community and may, therefore, increase the risk of becoming and remaining homeless (Caplan, Schutt, Turner, Goldfinger, & Seidman, 2006; Schutt, Seidman, Caplan, Martsinkiv, & Goldfinger, 2007; Solliday-McRoy, Campbell, Melchert, Young, & Cisler, 2004; Spence, Stevens, & Parks, 2004). Understanding and treating cognitive impairment in this population may be one crucial pathway to ending the cycle of homelessness for many individuals. In Canada, the term “homeless” generally refers to a “situation of an individual or family without stable, permanent, appropriate housing, or the immediate prospect, means and ability of acquiring it” (Canadian Homelessness Research Network, 2012). This definition encompasses varied living situations including unsheltered (e.g., living on the streets), emergency sheltered, provisionally accommodated and those at risk of homelessness (Canadian Homelessness Research Network, 2012). The definition of homelessness varies, however, in different cultures. For example, in Japan, the term “rough sleepers” is used for individuals who sleep in public spaces, whereas “the homeless” refers to all those who live in unstable accommodations (Okamoto, Hayakawa, Noguch, & Shinya, 2004). Memory is an important aspect of cognition (Lezak, Howieson, Loring, Hannay, & Fischer, 2004) and refers to the ability to encode, store and retrieve information (Baddley, 2002; Markowitsch, 2000; Rains, 2002). It has been asserted that memory can be implicit (unconscious or how system) or explicit (conscious or what system), and that explicit memory can further be divided into semantic and episodic memory. For example, a person may know how to ride a bike (implicit memory), what a bike is (semantic memory) or remember riding a bike to work (episodic memory). Short-term memory, the ability to hold information in mind for a short moment should be distinguished from working memory, or the ability to manipulate information in this buffer. In contrast, long-term memory may hold considerably more information. Finally, different elements

of memory can be impaired, such as visual– spatial, verbal and autobiographical memory (Lezak et al., 2004). Longitudinal (Cohen, Forbes, Mann, & Blanchard, 2006; Milev, Ho, Arndt, & Andreasen, 2005; Schutt et al., 2007) and cross-sectional (Green, Kern, Braff, & Mintz, 2000) studies have shown that deficits in memory may have wideranging implications for social functioning. For example, the inability to retain information may create barriers to maintaining employment and managing activities of daily living such as paying bills and managing finances, which can potentially lead to homelessness. Consequently, memory impairments may be a contributing factor leading to homelessness. A better understanding of the nature of memory deficits common to homeless persons is an important step in creating effective rehabilitation programmes that focus on memory remediation or compensation strategies. There are a variety of conditions that occur more frequently in homeless populations than the general public (Svoboda & Ramsay, 2013; Solliday-McRoy et al., 2004; Spence et al., 2004; Topolovec-Vranic et al., 2012) that further underscore the heterogeneity of the homeless population and that may contribute to the development of memory impairments. These include mental illness, substance abuse (e.g., chronic alcoholism; Lezak et al., 2004), infectious diseases such as HIV (Beijer, Wolf, & Fazel, 2012) and traumatic brain injury (TBI; Topolovec-Vranic et al., 2012). For example, individuals with schizophrenia are known to have significant cognitive impairments (Heaton et al., 2001). Similarly, HIV can lead to significant cognitive deficits (Heaton et al., 2010). Unfortunately, having a brain injury increases the likelihood of having another brain injury. As such, in addition to creating rehabilitation programmes to address memory problems in this population, efforts should be invested in prevention programmes aimed at preventing further cognitive impairments. These myriad of factors need to be considered when evaluating any literature related to cognitive functioning amongst this population. The purpose of this study was to systematically review the literature on memory deficits among populations of people who are homeless in order to gain a better understanding of its nature, causes and prevalence. Specifically, the following questions were explored:

MEMORY IMPAIRMENT AMONG PEOPLE WHO ARE HOMELESS

(1) How many published studies have examined memory functioning among people who are homeless? (2) What outcome measures were used to evaluate memory? (3) How common are memory deficits in the homeless samples studied? (4) What were the reported causes of or contributing factors to memory deficits in the homeless samples studied? (5) What was the reported temporal relationship between onset of memory deficits and onset of homelessness?

METHODS Data sources A literature search was conducted using keywords in MEDLINE/Pubmed (1966–2013), PsycINFO (1887–2011) and CINAHL (1983–2011), using the search terms: (“Homelessness” OR “Rooflesssness” OR “Homeless” OR “Hostel”) AND (“Memory” OR “Memory Deficit” OR “Memory Loss” OR “Cognitive” OR “Neuropsychological”). In addition to the computer search, manual searches were performed using reference lists from relevant papers. This search yielded five additional papers.

Selection criteria All identified titles and abstracts were screened and reviewed for relevance. Based on search criteria, articles were included if: (1) there was a sample of persons who were homeless; (2) memory was included as an outcome measure; and (3) a validated neuropsychological tool was used to measure memory. Only peer-reviewed journal articles were included. Articles were excluded if memory was not measured with a validated neuropsychological tool or if memory was measured with a tool assessing global cognitive functioning where scores on items relating to memory were not reported uniquely from other cognitive functions. For example, studies that used the mini mental state examination (MMSE; Folstein, Folstein, & McHugh, 1975) were excluded from this review as the MMSE measures memory in conjunction with other cognitive functions, and it only provides a global score of cognitive impairment, rather than an independent score for memory.

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Data extraction After screening for relevance, full papers were examined. Data on sampling, outcome measures, facet of memory explored and prevalance of memory impairment were extracted from all selected research studies. If a study included multiple samples, only data from the sample that was homeless would be reported on in the current review. For studies where participants were assigned to housing or cognitive remediation, only baseline data on measures of memory were included. A neuropsychologist (SR) interpreted the mean or median scores from each study according to the appropriate test norms. These findings are presented in Table 3. In some cases, it was not possible to interpret the scores based on the information provided in the included study. Additional information on sample performance in terms of proportion of the sample demonstrating impairment is provided in the notes section of Table 3.

Critical appraisal process The authors adopted a critical appraisal process used in a previous review (Burra et al., 2009) because this process is targeted at rating prevalence studies, a category under which the majority of studies in this review fell under. In the critical appraisal process, one point is allocated to each study for clearly defining the target population; using an unbiased sampling frame; assessing a sample size greater than 100; a response rate greater than 70%, or 80% if refusals were not described; use of valid and reliable neuropsychological tests; unbiased measurement or blinding, if applicable; reporting of confidence intervals and describing demographics of the sample in sufficient detail. Articles were given an overall rating of good (score 6–8), fair (score 4–5) or poor (score 0–3).

RESULTS A total of 106 abstracts were found and screened for inclusion based on search terms, and 11 of these articles were included for analysis in this review based on selection criteria (Figure 1). The critical appraisal ratings for included articles ranged between 1 (Medalia, Herlands, & Baginsky, 2003) and 7 (Seidman et al., 1997),

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Identified abstracts (n = 106) Not relevant (i.e., populations not homeless, memory functioning not assessed) (n = 76)

Assessed for outcome measure specific to memory (n = 30)

Excluded because memory was assessed with the MMSE, a global cognitive measure that does not produce a unique score for items of memory (n = 10)

Excluded papers (i.e., dissertation, review, book, etc.) (n = 5)

Excluded because memory was not assessed with a validated neuropsychological tool (n = 4)

Studies that explore memory deficit among homeless samples (n = 11) Figure 1. Consort diagram; MMSE, mini mental state examination.

and half of the studies were of poor or fair quality (Table 1). The majority of studies received low scores due to small sample sizes, low response rates and biased measurements or non-blinding where applicable. The remainder of the findings are presented according to the study aims.

How many published studies have exa‐ mined memory functioning among the homeless? The search yielded a total of 11 studies that measured memory impairment among samples of homeless persons using validated neuropsychological tools (Table 2). Four of the included studies (Caplan et al., 2006; Schutt et al., 2007; Seidman et al., 1997; Seidman et al., 2003) were part of the Boston McKinney Project, designed to test the effects of housing on the neuropsychological functioning of severely and persistently mentally ill homeless persons in Boston. In the

other studies, unique samples of homeless persons were assessed (Andersen et al., 2014; Bousman et al., 2010; Cotman & Sandman, 1997; Medalia et al., 2003; Pluck, Kwang-Hyuk, David, Spence, & Parks, 2012; Solliday-McRoy et al., 2004; Stergiopoulos, Burra, Rourke, & Hwang, 2011). In total, memory impairment was assessed across eight unique samples of persons who were homeless. The size of the samples ranged between 12 (Medalia et al., 2003) and 116 (Seidman et al., 1997). A total of 436 individuals who were homeless were assessed for memory difficulties. Across the unique samples studied, an estimated 318 individuals experienced a current or past mental illness. However, it should be noted that the way in which the presence of past or current mental illness was determined varied across studies. The majority of participants sampled were men with a mean age of 40.75 years old (mean ages in the samples ranged from 30.6 to 58.8 years). Women did not make up the majority of

TABLE 1 Critical appraisal scores of articles reviewed

Review article

Unbiased sampling frame

Sample size >100

Response rate greater than 70%

Use of valid and reliable neuropsychological tests

Unbiased measurement or blinding if applicable

Confidence intervals reported

Detailed description of sample

Overall score

1

1

0

0

1

1

0

1

5

Fair

0

1

0

1

1

1

1

1

6

Good

1

1

1

1

1

0

1

0

6

Good

0

0

0

0

1

0

1

1

3

Poor

0

0

0

0

1

0

0

0

1

Poor

1

0

0

0

1

0

1

1

4

Fair

1

1

1

0

1

0

1

1

6

Good

1

1

1

0

1

1

1

1

7

Good

1

1

0

0

1

0

1

1

5

Fair

0

0

0

0

1

0

1

1

3

Poor

1

1

0

1

1

1

0

1

6

Good

Overall rating

MEMORY IMPAIRMENT AMONG PEOPLE WHO ARE HOMELESS

Andersen et al. (2014) Bousman et al. (2010) Caplan et al. (2006) Cotman and Sandman (1997) Medalia et al. (2003) Pluck et al. (2012) Schutt et al. (2007) Seidman et al. (1997) Seidman et al. (2003) Solliday-McRoy et al. (2004) Stergiopoulos et al. (2011)

Target population clearly defined

699

700

TABLE 2 Characteristics of included studies

Research design; sampling methodology

34; 34 males; 58.8 (9.7); 24.0 (97.5) monthsa; 17 substance abuse; 14 mental illness; 12 TBI

An exploratory, quantitative study; convenience sampling in a homeless shelter

50; 28 males; 43 (36–50)a; 3 (1,5)b; n ranges between 8 and 23 for substance abuse (depending on substance); 41 mental illness; head trauma NR 112; 80 males; 37.5 (8.1); mean duration of homelessness NR; 69 substance abuse; 112 mental illness; head trauma NR 24; 13 males; 30.6 (6.5); mean duration of homelessness NR; 19 substance abuse; 2 mental illness; 2 head trauma

Case controlled study; participants in one of two groups (n = 50 “ever” homeless; n = 22 “never” homeless) and matched a priori on key characteristics Controlled field study; random assignment to group home or independent homes Cross-sectional study; recruitment from residential programme based on referrals from shelter staff

Prince George, a New York City based supportive housing programme Homeless services in Sheffield, England (including temporary hostels, day centres and meals services) Three homeless shelters in Boston, MA, for adults with mental illness Three homeless shelters in Boston, MA, for adults with mental illness Three homeless shelters in Boston, MA, for adults with mental illness Large homeless shelter in Milwaukee, WI

12; 6 males; 48.3 (NR); mean duration of homelessness NR; 12 substance abuse, mental illness or bothc; head trauma NR

Intervention with pre–post design; participants referred to study based on presence of cognitive impairment

80; 67 males; 35.2 (9.2); 67.5 (74.7) months; 32 substance abuse; 58 mental illnessd; head trauma NR

Cross-sectional study; participants contacted or referred to study by staff at homeless services

112; 80 males; 37.5 (8.1); mean duration of homelessness NR; 69 substance abuse; 112 mental illness; head trauma NR 116; 84 males; 37.6 (NR); 223 (401)e; 72 substance abuse; 116 mental illness; head trauma NR 91; gender NR; mean age NR; mean duration homeless NR; substance abuse NR; 91 mental illness; head trauma NR 90; 90 males; 40.96 (9.06); 87.68 days (75.55)f; 84 substance abuse/ dependence; 45 mental illness; 43 TBI

Controlled field study; random assignment to group home or independent homes Cross-sectional prevalence study; 303 persons screened, 156 agreed to participate and 118 were assigned housing Controlled field study; random assignment to group homes or independent apartments Cross-sectional study; voluntary participation

Acute psychiatric inpatient unit at St. Michael’s Hospital, Toronto, Canada

30; 22 males; 38 (12); 20 (15)g; 14 substance abuse; 30 mental illness; 13 head trauma

Cross-sectional study comparing homeless and housed participants; participants were referred by clinical staff based on chart diagnosis, housing history and capacity to give voluntary informed consent

Review article

Setting

Andersen et al. (2014)

A residential unit of a men’s homeless shelter in downtown Toronto, Canada Public, university-based psychiatric service in San Diego, CA

Bousman et al. (2010) Caplan et al. (2006) Cotman and Sandman (1997) Medalia et al. (2003). Pluck et al (2012)

Schutt et al. (2007) Seidman et al. (1997) Seidman et al. (2003) SollidayMcRoy et al. (2004) Stergiopoulos et al. (2011)

a

Three homeless shelters in Boston, MA for adults with mental illness An 18-month residential programme in Orange County, CA

Median, (interquartile range). Median number of episodes of homelessness (interquartile range). c All participants had histories of chronic psychiatric illness or substance abuse or both. d Fifty-eight participants reported past psychiatric contact, 20 reported a psychiatric hospital admission and all participants scored at levels of at least a “moderate” risk for problems of clinical significance on the Personality Assessment Screener (a measure of general psychopathology). e Mean number of days in transitional shelters was 223 (SD = 401). Of the subjects able to report total time spent homeless (N = 84), more than three-quarters of the sample (N = 64) reported being homeless for a year or more. A majority (N = 47) reported four or more years of homelessness. f Mean number of days that participants had stayed in a shelter during the previous four years. g Mean number of months that participants had been homeless in three years. b

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Sample size of homeless participants, n; gender; mean age (SD); mean duration of homelessness (SD); participants (n) with a history of: substance abuse; mental illness; head trauma or TBI

MEMORY IMPAIRMENT AMONG PEOPLE WHO ARE HOMELESS

participants in any study, and no studies specifically examined memory impairment in youth alone or in older adults. There was a great variation in settings and recruitment methods across these studies. Definitions of “homelessness” varied between studies. For example, Solliday-McRoy et al. (2004) considered participants staying in a shelter to be homeless, while others such as Bousman et al. (2010) defined homelessness as a dichotomous variable (“ever homeless” and “never homeless”) according to set criteria in the Stewart B. McKinney Act of 1987. In half of the studies, the average amount of time that participants had been homeless was not reported (Caplan et al., 2006; Cotman & Sandman, 1997; Medalia et al., 2003; Schutt et al., 2007; Seidman et al., 2003). How the duration of homelessness was reported also varied greatly between studies as can be seen in Table 2.

What outcome measures were used to evaluate memory? The validated neuropsychological tools used to assess memory across the 11 included studies varied and measured different facets of memory (Table 3). Neuropsychological measures assessing verbal memory were used in nine studies (Andersen et al., 2014; Bousman et al., 2010; Caplan et al., 2006; Cotman & Sandman, 1997; Schutt et al., 2007; Seidman et al., 1997; Seidman et al., 2003; Solliday-McRoy et al., 2004; Stergiopoulos et al., 2011). The most commonly used measure, the Wechsler Memory Scale (WMS), assessed learning, immediate and delayed recall as well as recognition (Wechsler, 1997, 2002). Five studies examined verbal memory using aspects of the WMS (Caplan et al., 2006; Cotman & Sandman, 1997; Schutt et al., 2007; Seidman et al., 1997; Seidman et al., 2003). There was variation across the studies using the WMS in terms of how test scores were reported on. For example, three of the five studies using the WMS reported a Verbal Memory index quotient (Cotman & Sandman, 1997; Seidman et al., 1997; Seidman et al., 2003), and two only reported on percentile scores from the Logical Memory subtest, which assessed memory of a short story (Caplan et al., 2006; Schutt et al., 2007). Memory for a word list was reported on in four studies. These studies used the Hopkins Verbal Learning Test-Revised (HVLT-R;

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Benedict, Schretlen, Groninger, & Brandt, 1998; Bousman et al., 2010; Stergiopoulos et al., 2011), the Rey Auditory Verbal Learning Test (RAVLT; Spreen & Strauss, 1998; Solliday-McRoy et al., 2004) and the California Verbal Learning Test (CVLT; Cotman & Sandman, 1997; Delis, Kramer, Kaplan, & Holdnack, 2004). These tools assess learning, immediate recall, delayed recall and recognition. Andersen et al. (2014) measured verbal memory using the Repeatable Battery for the Assessment of Neuropsychological Status (RBANS; Randolph, 1998). Anderson et al. reported on percentile scores from the Immediate Memory domain, a measure of verbal memory that includes a list-learning test and story-learning test. Visual memory was reported on in three studies (Cotman & Sandman, 1997; Medalia et al., 2003; Solliday-McRoy et al., 2004). SollidayMcRoy et al. (2004) used the Rey Complex Figure Test (RCFT; Osterrieth, 1944; Rey, 1941) to measure visual-spatial recall and recognition. Cotman and Sandman (1997) used the Benton Visual Retention Test (BVRT; Benton, Hannay, & Varney, 1975), and the Visual index score of the WMS-Revised (WMS-R; Wechsler, 2002). Cotman and Sandman also report baseline scores from a cognitive remediation programme called THINKable. THINKable is a software program that provides baseline scores of impairment in visual memory by testing subjects’ memory for order and location of objects on a screen. Medalia et al. (2003) implemented the memory scale from the Cognitive Stability Index (Erlanger & Feldman, 2000), a computerised test that purports to measure an individual’s ability to retain information over the short term. The test provides a memory slope score that represents the change in number of correct responses over four trials of a memory recognition test for hidden objects. In four studies (Andersen et al., 2014; Cotman & Sandman, 1997; Pluck et al., 2012; SollidayMcRoy et al., 2004) general or overall memory impairment was reported on. Solliday-McRoy et al. (2004) implemented the Neurobehavioural Cognitive status exam (Cognistat; Northern California Neurobehavioral Group, 1995), a brief screening tool that detects the presence of cognitive impairment in 10 areas and provides a separate score for memory impairment. Similarly, Pluck et al. (2012) only reported on general memory impairment. They used the WMS-III Abbreviated (Wechsler, 2002) and reported the findings from the Total Memory score and

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TABLE 3 Findings on memory impairment

Study

Measure(s)

Andersen et al. (2014)

RBANS

Bousman et al. (2010)

HVLT-R

Caplan et al. (2006)

WMS-revised delayed logical memory CVLT, BVRT A, Baseline version of the THINKable program,WMS-R delayed memory and verbal and visual indexes

Cotman and Sandman (1997)

Medalia et al. (2003)

Cognitive stability index

Verbal

Visual

Total memory score (visual and verbal)

RBANS immediate memory . Low average range (15.9%, range 0.1–82.0) RBANS delayed memory . Low average range (16.4%, range 0.1–79.0) HVLT-R list-learning test . Average rangea (T = 45, IQR, 30–51) HVLT-R delayed recall . Average rangea (T = 45, IQR, 3–54)

N/A

N/A

N/A

WMS-R logical memory (delayed) . Low average range (22.4%, SD = 22.1)

N/A

N/A

CVLT learning (trial 1–5) . Low average range (T = 43.7, SD = 1.4) WMS-R verbal index (immediate and delayed) . Average range (SS = 90.5, SD = 13.2)

N/A

BVRT A . Insufficient information available to interpret mean performance THINKable program baseline . Insufficient information available to interpret mean performance WMS-R visual index (immediate and delayed memory) . Average range (SS = 103.8, SD = 18.1)

WMS-R general memory . Average range (SS = 93.2, SD = 15.4) WMS-R delayed memory index . Average range (SS = 93.8, SD = 17.5)

Cognitive stability index . Insufficient information available to interpret mean performance

N/A

Note

On the HVLT-R, 40% demonstrated impairment in learning; 36% demonstrated impairment in recall

33% (n = 8) Demonstrated impairments in verbal, visual or delayed memory as determined by index scores on the WMSR of ≤85 BVRT A Mean correct = 6.4, SD = 2.3 Mean of all THINKable memory modules [Control group = 175.2 (SD = 63.0) and experimental group = 155.2 (SD = 52.5)] Cognitive stability index mean memory slope scores are within one SD of normative range. (mean memory slope scores = 7.139, SD NR)

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Findings

TABLE 3 (Continued) Findings

Study

Measure(s) WMS-III abbreviated

Schutt et al. (2007)

Delayed condition of the logical memory subtest from the WMS-R WMS-R verbal memory index score and immediate and delayed logical memory subtest

Seidman et al. (1997)

Seidman et al. (2003)

WMS-R verbal memory index, immediate and delayed logical memory subtest

Solliday-McRoy et al. (2004)

Cognistat; RAVLT; RCFT

Visual

N/A

N/A

Total memory score (visual and verbal)

WMS-R logical memory subtest (delayed) . Low average recall (22.4%, SD = 22.1)

N/A

WMS-III abbreviated total memory score . Low average range [SS = 85.1 (16.2)] WMS-II abbreviated general memory score . Average range [SS = 90.5 (14.7)] N/A

WMS-R logical memory (immediate) . Average range (25.6%, SD = 25.6) WMS-R logical memory (delayed) . Average range (24.4%, SD = 23.4). WMS-R verbal index (immediate and delayed) . Average range (SS = 80.7, SD = 17.5) WMS-R logical memory (immediate) . Low average range (23.2%, SD = 24.4) WMS-R logical memory (delayed) . Low average range (22.4%, SD = 22.1) WMS- R verbal index (immediate and delayed) . Borderline range (SS = 79.2, SD = 16.8) RAVLT learning (trial 1–5) . Borderline range (SS = 77.97, SD = 20.39) RAVLT immediate recall . Low average range (SS = 82.07, SD = 18.99) RAVLT delayed recall . Low average range (SS = 82.01, SD = 20.32) RAVLT recognition task (delayed) . Low average range (SS = 88.30, SD = 25.81)

N/A

N/A

N/A

N/A

RCFT immediate recall . Borderline range (SS = 74.89, SD = 20.15) RCFT delayed recall . Borderline range (SS = 73.70, SD = 20.46)

Cognistat . Insufficient information available to interpret mean performance

Note 55.4% scored below average or lower, with 18.9% scoring in the extremely low range on WMS-III abbreviated total memory

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64% with demons‐ trated impairment on the Cognistat (Mean score = 7.73, SD = 3.10) Percentage of participants scoring below average on RAVLT: . List learning (trial 1–5), 69% . Immediate recall 59% . Delayed recall 62% . Recognition task (delayed) 37%

MEMORY IMPAIRMENT AMONG PEOPLE WHO ARE HOMELESS

Pluck et al (2012)

Verbal

HVLT-R Stergiopoulos et al. (2011)

%, mean percentile score; BVRT, Benton Visual Retention Test; CVLT, California Verbal Learning Test; HVLT-R, Hopkins Verbal Learning Test-Revised; N/A, not applicable; R, revised; RBANS, Repeatable Battery for the Assessment of Neuropsychological Status; RAVLT, Rey Auditory Verbal Learning Test; RCFT, Rey–Osterrieth Complex Figure Test; SD, standard deviation; SS, mean standard score; ss, mean scale score; T, mean T-score; WMS, Wechsler Memory Scale. a Median T-score.

N/A . Insufficient information available to interpret mean performance

N/A

Visual Study

TABLE 3 (Continued)

Measure(s)

Findings

Verbal

Total memory score (visual and verbal)

Percentage of participants scoring below average on RCFT: . Immediate recall 78% . Delayed recall 76% Delayed recall mean = 6.8, SD = 3.2 Recognition mean = 9.5, SD = 1.9

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Note

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General Memory score. Cotman and Sandman (1997) also provided a General Memory score and Delayed Memory score from the WMS-R. In addition to the Immediate Memory domain percentile scores which measures verbal memory, Andersen et al. (2014) reported findings from the RBANS Delayed Memory domain, which encompasses both delayed verbal and visual recall and recognition.

What was the reported prevalence of memory deficits in the samples of homeless persons studied? Deficits in verbal memory. Overall, verbal memory impairments were frequent, but inconsistent, among homeless persons (Table 3). In the Boston McKinney sample, scores on the WMS-R were in the average and low average ranges (Caplan et al., 2006; Schutt et al., 2007; Seidman et al., 1997; Seidman et al., 2003). Though not impaired, the scores represent a departure from normal memory functioning. Cotman and Sandman (1997) reported a mean Verbal index score of 90.5 (SD = 13.2) on the same measure, which is considered to be in the average range. Cotman and Sandman also reported that 33% of their sample had at least one index Standard Score on Visual, Verbal or Delayed memory that was below 85, a score considered in the low average range or lower. In line with the Boston McKinney findings, Andersen et al. (2014) reported mean percentile rank scores on the Immediate Memory domain of the RBANS in the low average range [mean percentile rank of 15.9% (range 0.1–82.0)]. The use of wordlists yielded more consistent findings. Using the HVLT-R, Bousman et al., (2010) found that 40% of their sample had impaired learning and 36% had impaired recall. The median scores from their sample were considered to be in the average range. Stergiopoulos et al. (2011) reported mean Total Recall scores that were two standard deviations below normative scores (Benedict et al., 1998). However, the mean scores from their study could not be interpreted based on the information presented in the paper. Cotman and Sandman’s (1997) sample performed in the low average range on the CVLT (M = 43.7, SD = 1.4).Using the RAVLT, Solliday-McRoy et al. (2004) determined that deficits in new verbal learning abilities and immediate recall were probable in 69% and 59% of their sample, respectively. They noted

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that 62% had probable deficits on delayed verbal recall while 37% had probable deficits in delayed verbal recognition. Their sample mean scores on the RAVLT were in the borderline and low average ranges. Visual memory. There was discrepancy in findings across studies assessing visual memory difficulties among people who are homeless. Using the RCFT, Solliday-McRoy reported that 78% of their sample obtained standard scores in the low average to extremely low range on immediate visual recall and 76% obtained standard scores in the low average to extremely low range on delayed visual recall. Mean scores from their sample were considered to be in the borderline range. Cotman and Sandman (1997) reported mean Visual Memory index scores on the WMSR in the average range (M = 103.8; SD = 18.1). Again, despite the overall average performance in the visual modality, 33% of the sample scored below 85 on the Verbal, Visual or Delayed memory index of the WMS-R, scores considered to be in the low average range. Cotman and Sandman reported BVRT mean errors scores of 5.6 (SD = 4.9) and mean correct scores of 6.4 (SD = 2.3). These scores are poorer than expected based on the sample mean IQ, leading Cotman and Sandman to conclude that participants in their sample did demonstrate visual memory impairment. Cotman and Sandman also reported the mean of all of the THINKable modules from their sample’s baseline testing. However, there was limited information available in the study for the sample mean scores to be interpreted. Using the Cognitive Stability Index, a computerised test of visual memory, reaction time, attention and processing speed, Medalia and colleagues found a mean memory slope that fell in the normative range based on the mean age (M = 48.3) of sample participants (Erlanger et al., 2002). General memory impairment. There were more consistent findings across the studies reporting on general memory impairment among homeless persons. One of the four studies that examined general memory deficits did not report memory impairment among their sample (Cotman & Sandman, 1997). Cotman and Sandman reported average scores on the WMS-R General Memory and Delayed Memory indexes. Again, they noted that 33% of their sample obtained a below average score on Visual, Verbal or Delayed memory indexes. In comparison, Pluck et al.

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(2012) reported mean Total Memory scores on the WMS-III that fell in the low average range. Specifically, Pluck and colleagues found 55.4% of Total Memory scores were in the low average to extremely low range, with 18.9% in the extremely low range. Similarly, using the Cognistat, Solliday-McRoy et al. (2004) discovered that 22% of their sample demonstrated severe memory impairment, 24% moderate memory impairment, 18% mild memory impairment and 36% average memory performance. Using the RBANS, Andersen et al. (2014) report mean Delayed Memory percentile scores, scores which reflect both visual and verbal delayed memory, that also fell in the low average range.

What were the reported causes of mem‐ ory deficits in the homeless samples studied? In seven studies (Andersen et al., 2014; Bousman et al., 2010; Caplan et al., 2006; Pluck et al., 2012; Seidman et al., 2003; Solliday-McRoy et al., 2004; Stergiopoulos et al., 2011) and across six unique samples, possible causes of or contributing factors to memory deficits were examined. These factors were the state of homelessness, TBI, substance abuse history and mental illness (Table 4). Homelessness. The impact of homelessness on memory was explored in five studies (Bousman et al., 2010; Caplan et al., 2006; Pluck et al., 2012; Seidman et al., 2003; Stergiopoulos et al., 2011) that revealed contradicting results (Table 4). Two of these studies were part of the Boston McKinney Project (Caplan et al., 2006; Seidman et al., 2003). By testing homeless participants after assigning them to stable housing conditions (independent apartments or group homes), the researchers were able to speculate on the effects of homelessness on memory impairment. Assessment of the homeless participants at 18 and 48 months (Caplan et al., 2006; Seidman et al., 2003) after being assigned to housing revealed significant improvement on verbal memory scores for both participants assigned to group homes and independent apartments. The researchers concluded that stable housing may be a factor contributing to improvement in participants’ memory, whereas homelessness may have impaired it. In contrast, Pluck et al. (2012) used the Wechsler Adult Test of Reading (Wechsler, 2001) to estimate pre-homeless memory test

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Review article

Variable(s) explored

Andersen et al. (2014)

TBI

Bousman et al. (2010)

Homelessness, number of homelessness episodes

Caplan et al. (2006) Pluck et al. (2012)

Homelessness

Seidman et al. (2003) SollidayMcRoy et al. (2004)

Homelessness

Stergiopoulos et al. (2011)

Homelessness, substance abuse, mental illness

Substance abuse, mental illness, TBI, length of loss of consciousness associated with TBI Homelessness

How were the variables measured?

Findings

The Brain Injury Screening Questionnaire (BISQ) was used to assess likelihood of a history of TBI. The Wilcoxon Rank Sum test was used to compare RBANS percentile scores between those with a positive screen for TBI according to the BISQ and those with negative screens according to the BISQ Wilcoxon tests between the control group of never-homeless persons to the group of persons who had been homeless. Associations between number of homelessness episodes and individual tests and domains were explored Participants assigned to stable housing conditions and re-assessed for memory impairment at 18 months and 48 months Comparison of pre-homeless estimates of memory and IQ to current memory and IQ. ANOVAs were used to compare memory scores between those with past mental psychiatric contact and those without and to compare those with past-year daily use of heroin or crack cocaine to those without

No significant differences were found on the percentile ranks on the Immediate Memory or Delayed Memory scores from the RBANS between the groups

Participants assigned to stable housing conditions and re-assessed for memory impairment at 18 months ANOVAs between those who did and did not report history of substance abuse, mental illness, or TBI; correlations between lengths of loss of consciousness associated with TBI Independent samples t-tests were used to compare the scores of homeless and housed participants on each measure of memory

No significant differences between the “ever” and “never” homeless group on recall. No significant correlations between test scores and number of homelessness episodes When participants were given stable housing, memory scores improved Homelessness: General memory was significantly lower than the estimated pre-homeless score. There was a greater drop in memory function in comparison to general intellectual functioning from pre-homeless estimates to current functioning. However, there were no significant correlations with Total Memory scores for either the total months spent homeless over the lifetime or total months of the current homeless episode. Substance abuse and mental illness: There were no significant associations between pastyear substance misuse or past psychiatric contact with memory scores When participants were given stable housing, memory scores improved No significant between-group differences on memory scores between those with a history of TBI compared to those without. No significant correlations between lengths of loss of consciousness associated with TBI and memory scores There were no significant differences on any of the measures of memory between the two groups

ENNIS, ROY, TOPOLOVEC-VRANIC

TABLE 4 Studies that explored variables potentially associated with memory impairment among homeless people

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scores. While they found a significant drop in memory function from pre-homeless times to current functioning, they reported that duration of homelessness was not significantly correlated with memory scores. Therefore, their study was unable to provide support for the notion that homelessness itself was the reason for cognitive decline (Pluck et al., 2012). Bousman et al. (2010) and Stergiopoulos et al. (2011) report similar conclusions. Bousman and colleagues used the HVLT-R to assess and compare persons presenting at a publicly funded psychiatric service who had reported that they had experienced homelessness to those who had not experienced homelessness. After being matched for age, sex, ethnicity, education, substance abuse/dependence and psychiatric morbidity, no significant differences between the two groups were found (Bousman et al., 2010). Stergiopoulos et al. (2011) also compared scores of homeless and housed adults with schizophrenia or schizoaffective disorder on the HVLT-R. Similarly, they reported no significant differences on measures of memory between the two groups. TBI. In two studies, TBI was explored as a possible contributor to memory deficit among homeless populations (Andersen et al., 2014; Solliday-McRoy et al., 2004). Solliday-McRoy et al. (2004) found that 43 homeless participants (48%) self-reported a history of TBI. An analysis of variance was used to compare participants with a history of TBI to those who had no history of head trauma on measures of memory. No significant between-group differences were found, leading the researchers to conclude that TBI may not contribute to the memory deficits observed among their homeless sample. As well, a regression analysis was run to assess if participants’ length of loss of consciousness associated with TBI correlated with their memory tests. No significant results were found (Solliday-McRoy et al., 2004). Andersen et al. (2014) assessed men (n = 34) in a residential unit of an urban homeless shelter using the Brain Injury Screening Questionnaire, a self-reported tool that provides users with a screen for the probability of a previous TBI. They compared performance on the RBANS between those with a positive screen for TBI to those with a negative screen for TBI and reported no significant between group differences on either of the memory domain scores.

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Substance abuse and mental illness. Substance abuse and mental illness were examined in relation to memory impairment in homeless persons in two studies (Pluck et al., 2012; Solliday-McRoy et al., 2004). In both studies, substance abuse and mental illness were determined through selfreported health history. Both studies used analysis of variance to compare persons with a history of substance abuse or mental illness to those with no history on measures of memory and neither study detected significant between group differences.

On the temporal relationship between onset of memory deficits and onset of homelessness The temporal relationship between onset of memory deficits and onset of homelessness was explored in one study (Pluck et al., 2012). Using the Wechsler Test of Adult Reading to estimate pre-homeless memory scores, Pluck and colleagues determined that homeless participants in their study suffered a drop in cognitive function on both tests of memory and IQ, and they reported that the magnitude of the drop in memory scores was significantly greater than for IQ. The researchers concluded that the reduction in cognitive function may have happened during homelessness or prior to it (Pluck et al., 2012).

DISCUSSION Despite the scarcity of research examining memory impairment among homeless persons using validated neuropsychological assessment tools, the majority of studies that measure memory impairment among people who are homeless suggest that memory deficits are common in this population. Considering the limited findings across these studies, the heterogeneous samples used, the variation in neuropsychological tools used and the poor to fair quality of the research, it seems that few studies exist (only 11 studies found in this review) that used validated neuropsychological tools to assess memory impairment among people who were homeless. As well, very little is known about the factors that contribute to memory impairment in persons who are homeless and the relationship between the onset of homelessness and the onset of memory problems. These findings will be discussed in terms of how they relate to the study aims.

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Studies that measured memory deficits in homeless persons Only 11 studies, using eight samples consisting of a total of 436 persons, reported on the prevalence of memory impairment among people who are homeless. In comparison to the number of people globally (United Nations Comission on Human Rights, 2005) who experience homelessness, the amount of persons sampled across these studies is minimal. Moreover, compared to the vast amount of research on the prevalence of other adversities among people who are homeless, such as mental illness (Koegel, Burnam, & Baumohl, 1996) and substance abuse (Fichter et al., 1996), the amount of research on the prevalence of memory impairment among people who are homeless is scarce. Not only have few studies examined memory impairment, but also across these studies samples were not necessarily representative of the homeless population at large, making it difficult to generalise the findings. The majority of the samples were taken from the USA (Bousman et al., 2010; Caplan et al., 2006; Cotman & Sandman, 1997; Medalia et al., 2003; Schutt et al., 2007; Seidman et al., 1997; Seidman et al., 2003; Solliday-McRoy et al., 2004) and from homeless shelters or hostels (Andersen et al., 2014; Caplan et al., 2006; Cotman & Sandman, 1997; Medalia et al., 2003; Schutt et al., 2007; Seidman et al., 1997; Seidman et al., 2003; Solliday-McRoy et al., 2004), rather than on the street. People who live on the street may have a different level of cognitive function as compared to those who live in homeless shelters. Also, women, youth, children and the elderly who were homeless were not adequately represented in the included studies. The samples were primarily composed of adult men. It is clear that not only is more research needed on the level of memory impairment among persons experiencing homelessness, but also more persons from different settings need to be assessed and more women and youth should be included in future studies.

Methods of assessing memory impair‐ ment There is a lack of controlled study designs among research in this area. Cross-sectional designs were used in the majority of the studies and nonhomeless control groups were only used in two studies (Bousman et al., 2010; Stergiopoulos et al.,

2011). In both studies, groups of people who were homeless were compared to samples of individuals who were housed. Greater use of controlled research designs in studies of homeless populations is necessary due to the many confounding demographic variables in this population. There was variation in the methods and tools used to assess memory impairment among people who are homeless, rendering it hard to make comparisons between study findings. The current review identified 11 studies that used validated neuropsychological tools to measure memory impairment among people who are homeless. The tools used across these studies varied widely. Even among studies using the WMS as a measure of memory, scores from different components of the test were reported. In addition to the included studies, three papers were identified that assessed memory without validated neuropsychological tools among people who are homeless. Across these three studies (Crane, 1993; Hux, Schneider, & Bennett, 2009; Stergiopoulos & Herrmann, 2003), there was discrepancy in the way that memory was defined and measured. Specifically, deficits in memory were measured through self-report questionnaires (Hux et al., 2009), unstructured interviews (Crane, 1993) and surrogate reports from homeless shelter directors (Stergiopoulos & Herrmann, 2003). Memory impairment was defined vaguely as “problems remembering” (Hux et al., 2009), “inconsistency in answers” (Crane, 1993) or “memory impairment” (Stergiopoulos & Herrmann, 2003). Due to the variation across these studies, it was difficult to compare research findings with those from studies using validated neuropsychological tools to assess memory.

Prevalence of memory impairment In general, the studies reviewed reported impairment in general or overall memory and in verbal memory with conflicting findings regarding visual memory problems among homeless persons. In the majority of studies that examined verbal and overall or general memory impairment significant impairment was observed. The one study that did not report significant impairment across general memory and verbal memory measures was conducted by Cotman and Sandman (1997) whose sample mean scores fell in the average range. However, their sample was small (n = 24), and they still reported that 33% of the participants

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scored below average on at least one of the memory indexes of the WMS-R. One possible reason why Cotman and Sandman’s sample may have performed better than others on measures of verbal memory is that participants were recruited from a residential programme for homeless persons that “only accepts clients who are judged by staff as being potentially employable” (Cotman & Sandman, 1997, p.17). Importantly, persons with mental illness or developmental delay were excluded from this programme. This programme was also designed to help clients restructure their educational and job goals and offered on-site high school and basic skills classes. Given the specificities of the population from which Cotman and Sandman recruited, it is likely that participants were generally better functioning than those in other samples, who were recruited from other types of homeless shelters or the streets. Less agreement was found among the studies that explored visual memory functioning. In two studies (Cotman & Sandman, 1997; Medalia et al., 2003) reported mean scores of general memory fell in the average range or within one standard deviation of the normative range (Medalia et al., 2003). In contrast, Solliday-McRoy et al. (2004) reported high rates of visual memory impairment in their sample. The two studies (Cotman & Sandman, 1997; Medalia et al., 2003) that did not find visual memory to be impaired used the smallest samples of homeless persons among the studies included in the review. Specifically, Medalia et al. (2003) only sampled 12 persons, while Cotman and Sandman (1997) sampled 24. Making conclusions regarding the prevalence of memory impairments among people who are homeless is difficult because of the variation in the measures used to assess memory, the discrepancies between the ways that scores were reported and the limited sample sizes used across the studies.

Studies that explored reported causes or conditions related to memory loss It was also difficult to make conclusions about the factors that may contribute to memory impairment in people who are homeless. There were a limited number of studies in this area and incongruent findings across these studies. Variables that may relate to or cause memory impairment

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in people who are homeless were only explored in seven studies. Although neither substance abuse nor mental illness was found to be related to memory impairment, both studies reporting on this relied on self-reported health history to determine if participants had mental illness or substance abuse problems, rather than validated tools of assessment. With no replication studies, it is difficult to determine whether substance abuse or mental illness contributes uniquely to memory impairment observed in homeless persons. In six of the 11 studies included for review, all participants had a mental illness. In three of the five studies, where the sample was not solely composed of persons with mental illness, a majority of participants were found to have mental illness. Therefore, it is possible that the high prevalence of memory deficits reported in the included studies may be a reflection of the high prevalence of mental illness in the samples studied. Mental illnesses such as schizophrenia can also affect cognitive function and may contribute to deficits in memory obser‐ ved in this population (Heaton et al., 2001). The effects of homelessness on memory impairment were examined in four unique samples and in five studies (Bousman et al., 2010; Caplan et al., 2006; Pluck et al., 2012; Seidman et al., 2003; Stergiopoulos et al., 2011), and the findings are conflicting. The two studies (Caplan et al., 2006; Seidman et al., 2003) that reported on the same sample of homeless persons with mental illness in Boston revealed that once participants were moved to stable housing, their verbal memory scores improved. Consequently, the researchers commented that stable housing may improve memory functioning and homelessness may impair it. However, participants’ pre-homeless memory functioning was not assessed. As well, no control groups of people who are homeless with similar diagnoses of mental illness and substance abuse were assessed in order to determine if other confounding variables may have been responsible for such findings. Therefore, there are limited grounds to infer that the state of being homeless can impair memory functioning. Pluck and colleagues found a drop in Total Memory scores from current functioning to prehomeless estimates (Pluck et al., 2012). However, duration of homelessness did not significantly correlate with Total Memory scores, and the researchers could not make conclusions as to whether impairment in memory occurred during or prior to homelessness. It is possible that

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individuals in their sample experienced memory impairment before the onset of homelessness as a result of another condition (e.g., substance abuse, mental illness and chronic illness) and memory impairment could have contributed to homelessness as opposed to being a consequence of homelessness. Bousman et al. (2010) and Stergiopoulos et al. (2011) assessed the effects of homelessness on memory impairment using a control group matched on possible confounding variables and found that memory impairment between the groups was not different. Most likely, memory impairment is both a contributing factor to and consequence of being homeless. People who are homeless may have limited access to cues that could orient them to time and place, such as access to the news, television or radio and this may be confusing and lead to difficulty remembering. Alcohol abuse, chronic illness, malnutrition and mental illness may also contribute to both homelessness and memory impairment. The effects of TBI on memory impairment was only explored in two studies (Andersen et al., 2014; Solliday-McRoy et al., 2004). SollidayMcRoy and colleagues reported TBI among 48% of their sample but determined that TBI was not correlated with memory impairment. However, TBI history was assessed using selfreport. Andersen et al. (2014) also used a selfreported screening tool to assess for a history of TBI and reported no significant association between TBI history and memory impairment. However, their sample size was small, and they reported overall low scores in these domains across their entire sample. There may have been a floor effect or limited power to detect between group differences in their study. More studies on the effects of repeated mild TBI and other sources of acquired brain injury, such as HIV, stroke and Hepatitis-C should be conducted in the future.

Temporal relationship between onset of homeless and onset of memory deficits An understanding of whether memory impairment precedes homelessness is valuable as it helps clarify whether memory impairment may lead to homelessness or may result from homelessness. Unfortunately, this relationship was only examined in one study (Pluck et al., 2012) that could not make conclusions as to whether memory impairment occurred prior to or during

homelessness. An understanding of whether memory problems can lead some individuals into homelessness is crucial. As the world’s population ages (Anderson & Hussey, 2000), there may be an epidemic of Alzheimer’s disease, which substantially impairs memory function (Smith & Knight, 2002). At the same time, there is speculation that some countries are not well prepared to handle the financial costs of caring for elderly populations (Anderson & Hussey, 2000) who are most often dependent on pensions. This could mean that, in the future, persons who have Alzheimer’s may not be able to receive as much social assistance and that such diseases could precipitate homelessness.

Recommendations for future studies The current review has not only shown that more research is needed on the topic of memory impairment among people experiencing homelessness, but it has also highlighted the need for more rigorous research in this area. Through both the critical appraisal of the current literature and the discussion of the limitations among the research studies, it is possible to speculate on ways that future studies could be improved. There was a great deal of variation in tools used to measure memory function among persons who are homeless. Greater consistency is needed in the methods and measures used to evaluate memory impairment in this population. Most studies reviewed lacked unbiased measurement or blinding, large sample sizes and high response rates (Table 1). In order to alleviate bias in sampling and to increase sample sizes, future researchers should consider sampling many individuals from multiple sites. Not all persons who are homeless live on the street or in shelters; some seek temporary shelter in cars, abandoned buildings or railroads (Hegerty, 2009). Moreover, there are different types of shelters, such as shelters for the mentally ill, youth shelters and women’s shelters. In prospective studies, samples should be recruited from a multitude of these sites in order to assess a more representative sample of people who are homeless. In future studies the relationship between substance abuse, TBI, mental illness, the state of homelessness and memory impairment must be thoroughly explored. Validated tools should be used to assess each of these variables. For example, mental illness could be assessed using a diagnostic

MEMORY IMPAIRMENT AMONG PEOPLE WHO ARE HOMELESS

interview. Whenever possible, chart reviews should be conducted in addition to self-report. In order to determine the unique contributions of mental illness to deficits in memory in this population, persons who experience homelessness and mental illness should be compared to those who experience homelessness and no mental illness. In light of the significant prevalence of TBI reported amongst persons who are homeless (Andersen et al., 2014; Hwang et al., 2008; Solliday-McRoy et al., 2004; Topolovec-Vranic et al., 2012) and the strong association between memory impairment and TBI in the general population, it is important that more research be conducted on the effects of TBI on memory impairment among individuals who are homeless. While there is a great deal of research on substance abuse and mental illness in this population (Koegel et al., 1996), less is known about the effects of TBI. Interestingly, recent research has shown that many of the symptoms associated with mental illness and substance abuse are also common to Post-Concussive Syndrome (Lo, 2001). This makes it easy to misdiagnose or mistake behaviours that actually result from TBI as being signs of mental illness or substance abuse. For example, a worker in a homeless shelter could interpret the behaviours of a client exhibiting post-concussive symptoms such as poor concentration, irritability and mood swings as resulting from alcohol abuse, when in fact the individual has a history of unidentified TBI. More research using comprehensive neuropsychological tests as well as clinical interviewing and detailed analysis of medical and social histories would be useful in teasing out the potential role of brain injury on memory deficits among populations of people who are homeless.

CONCLUSION Although the small body of literature included in this review reveals significant levels of memory impairment among people experiencing homelessness, very little is known about memory impairment and the factors that may contribute to observed deficit. Due to the social implications associated with memory function, it is important that more controlled research be conducted in this area.

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