Journal of Affective Disorders 174 (2015) 353–360

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Disability in bipolar I disorder: The 36-item World Health Organization Disability Assessment Schedule 2.0 Georgina Guilera a,b, Juana Gómez-Benito a,b,n, Óscar Pino a,c, Emilio Rojo c, Eduard Vieta d, Manuel J. Cuesta e, Scot E. Purdon f, Miguel Bernardo g, Benedicto Crespo-Facorro h, Manuel Franco i, Anabel Martínez-Arán f, Gemma Safont j, Rafael Tabarés-Seisdedos k, Javier Rejas l, for the Spanish Working Group in Cognitive Function a

Department of Methodology, Faculty of Psychology, University of Barcelona, Barcelona, Spain Institute for Brain, Cognition, and Behavior (IR3C), Granollers Hospital General, Granollers, Barcelona, Spain Department of Psychiatry, Benito Menni CASM, Granollers Hospital General, Granollers, Barcelona, Spain d Bipolar Disorders Program, Institute of Neuroscience, Hospital Clinic i Provincial, IDIBAPS, CIBERSAM, University of Barcelona, Barcelona, Spain e Psychiatric Hospitalization Unit, Hospital Virgen del Camino, Pamplona-Iruña, Spain f Department of Psychiatry, Bebensee Schizophrenia Research Unit, University of Alberta, Edmonton, AB, Canada g Barcelona Clinic Schizophrenia Unit, Institute of Neuroscience, Hospital Clinic de Barcelona, IDIBAPS, University of Barcelona, CIBERSAM, Barcelona, Spain h University Hospital Marqués de Valdecilla, IDIVAL, School of Medicine, University of Cantabria, Spain and CIBERSAM, Santander, Spain i Department of Psychiatry, Hospital Provincial Rodríguez Chamorro, Zamora, Spain j Psychiatry Unit, Hospital Universitari Mútua Terrassa, Terrassa, Spain k Teaching Unit of Psychiatry and Psychological Medicine, Department of Medicine, University of Valencia, CIBERSAM, Valencia, Spain l Health Outcomes Research Department, Medical Unit, Pfizer Spain, Alcobendas, Madrid, Spain b c

art ic l e i nf o

a b s t r a c t

Article history: Received 17 July 2014 Received in revised form 5 December 2014 Accepted 9 December 2014 Available online 17 December 2014

Background: The WHODAS 2.0 is an ICF-based multidimensional instrument developed for measuring disability. The present study analyzes the utility of the 36-item interviewer-administered version in a sample of patients with bipolar disorder. There is no study to date that analyses how the scale works in a sample that only comprises such patients. Methods: A total of 291 patients with bipolar disorder (42.6% males) according to DSM-IV-TR criteria from a cross-sectional study conducted in outpatient psychiatric clinics were enrolled. In addition to the WHODAS 2.0, patients completed a comprehensive assessment battery including measures on psychopathology, functionality and quality of life. Analyses were centered on providing evidence on the validity and utility of the Spanish version of the WHODAS 2.0 in bipolar patients. Results: Participation domain had the highest percentage of missing data (2.7%). Confirmatory factorial analysis was used to test three models formulated in the literature: six primary correlated factors, six primary factors with a single second-order factor, and six primary factors with two second-order factors. The three models were plausible, although the one formed by six correlated factors produced the best fit. Cronbach’s alpha values ranged between .73 for the Self-care domain and .92 for Life activities, and the internal consistency of the total score was .96. Relationships between the WHODAS 2.0 and measures of psychopathology, functionality and quality of life were in the expected direction, and the scale was found to be able to differentiate among patients with different intensity of clinical symptoms and work situation. Limitations: The percentage of euthymic patients was considerable. However, the assessment of euthymic patients is less influenced by mood. Some psychometric properties have not been studied, such as score stability and sensitivity to change. Conclusions: The Spanish version of the 36-item WHODAS 2.0 has suitable psychometric properties in terms of reliability and validity when applied to patients with bipolar disorder. Disability in bipolar patients is especially prominent in Cognition, Getting along, Life activities, and Participation domains, so functional remediation interventions should emphasize these areas in order to improve the daily living activities of these patients. & 2014 Elsevier B.V. All rights reserved.

Keywords: Disability Functioning Bipolar I disorder WHODAS 2.0 ICF Health status

n Correspondence to: Departament de Metodologia de les Ciències del Comportament, Facultat de Psicologia, Universitat de Barcelona, Passeig de la Vall d’Hebron 171, 08035 Barcelona, Spain. Tel.: þ34 933125082; fax: þ 34 934021359. E-mail address: [email protected] (J. Gómez-Benito).

http://dx.doi.org/10.1016/j.jad.2014.12.028 0165-0327/& 2014 Elsevier B.V. All rights reserved.

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G. Guilera et al. / Journal of Affective Disorders 174 (2015) 353–360

1. Introduction Bipolar disorder and severe mental disorders in general are among the most incapacitating diseases for patients who suffer from them. The 2000–2012 Global Burden of Disease study (World Health Organization, 2014) establishes that among the entire population with disability (i.e., estimation of years due to disability), bipolar disorder is the sixth and third cause in men and women, respectively. Although perhaps studied less frequently than other types of psychosis such as schizophrenia, as a result of its high prevalence and severity, several studies have undertaken to determine the neurocognitive and psychosocial factors involved in the degree of disability of patients with bipolar disorder (Bonnín et al., 2010; Burdick et al., 2010; Depp et al., 2012).However, some questions remain unanswered regarding the predictive variables of disability in bipolar disorder and to what extent they contribute to this prediction. Most authors nevertheless agree that several variables are at play, such as psychotic symptoms, mood, social competence, intrinsic motivation, cognitive function, daily living skills, and family and social support (Depp et al., 2010; Elgie and Morselli, 2007; Green, 2006; Huxley and Baldessarini, 2007; Iosifescu, 2012; Johnson et al., 2003; Judd et al., 2005; Martinez-Arán et al., 2007; Reinares et al., 2013; Tabarés-Seisdedos et al., 2008; Wingo et al., 2009).The most recent studies even establish direct and indirect relationships between functionality, these and other variables, with the aim of proposing explanatory models (Bowie et al., 2010; Giglio et al., 2010; Bonnín et al., 2014a). Patients with bipolar disorder tend to have difficulties at several levels (Elgie and Morselli, 2007; Judd et al., 2008). For example, their productivity at work is often decreased and they are dismissed more often (Bonnín et al., 2014b); they generally have fewer social interactions and a reduced social network and therefore have less likelihood of accomplishing social milestones such as marriage (Rosa et al., 2009); they find it difficult to express their opinions and to communicate comfortably; and they show persistent problems in carrying out daily activities such as certain domestic tasks. In short, patients with bipolar disorder have problems in a wide range of diverse day-to-day situations. Given that it affects overall patient life, functionality becomes a key aspect to be incorporated into the assessment of treatment effectiveness, as even though patients with bipolar disorder may be in symptomatic remission or recovery, they may continue to present difficulties at a functional level (Calabrese et al., 2003; Rosa et al., 2008, 2010). To incorporate all these aspects into the functionality assessment process for patients diagnosed not only with bipolar disorder but with any disease, the World Health Organization (WHO) developed in a worldwide comprehensive consensus process, a biopsychosocial model called the International Classification of Functioning, Disability and Health (ICF; World Health Organization, 2000) that aims to provide a conceptual context for describing and classifying the health status of individuals, taking into consideration body functions and structures, activities and participation and environmental factors. As the ICF system is difficult and complex to use in daily clinical practice, the WHO developed the ICF Checklist and Disability Assessment Schedule 2.0 (WHODAS 2.0; Üstün et al., 2010; World Health Organization, 2000). The WHODAS 2.0 has been received with great success; it is now available in more than 10 different languages and the psychometric properties of its different versions have been studied in community population (Kim et al., 2005; Sousa et al., 2010; Von Korff et al., 2008) as well as in various conditions such as depression and back pain (Chwastiak and Von Korff, 2003), depression (Luciano et al., 2010a, 2010b, 2010c), schizophrenia (Chopra et al., 2004; Guilera et al., 2012; McKibbin et al., 2004; Pyne et al., 2003) schizophrenia and multiple sclerosis (Chopra et al., 2008), inflammatory arthritis (Baron et al., 2008), patients with systemic sclerosis (Hudson et al., 2008), spinal cord

injury (De Wolf et al., 2012), adults with motor, mental or sensory disability (Federici et al., 2009), anxiety disorders (Perini et al., 2006), breast cancer (Zhao et al., 2013), rehabilitation patients (Pösl et al., 2007), adults with acquired hearing loss (Chisolm et al., 2005), and 13 physical and mental chronic conditions including 114 patients diagnosed with bipolar disorder (Garin et al., 2010). In general, these studies coincide in concluding that the WHODAS 2.0 is an easy-to-apply instrument for validly and reliably assessing individuals’ functionality and disability, and have been proposed as the standard tool for measuring functioning by the DSM-5 and the forthcoming ICD-11. This study goes one step further in the assessment of WHODAS 2.0 by studying for the first time the utility of the 36-item interviewer-administered version in an extensive sample formed only by patients with bipolar disorder1. Based on the studies published to date, the hypotheses pertaining to the validity of the WHODAS 2.0 are: (1) dimensional structure will adjust to that proposed by the creators of the instrument, assuming six disability factors (World Health Organization, 2000); (2) WHODAS 2.0 scores will be significantly related to levels of depression (Baron et al., 2008; Chwastiak and Von Korff, 2003; McKibbin et al., 2004), illness severity (Bottlender et al., 2013; Luciano et al., 2010a; Pösl et al., 2007), social and occupational functioning (Hudson et al., 2008; Lee et al., 2013; Pösl et al., 2007) and health-related quality of life (Chávez et al., 2005; Luciano et al., 2010b; Quintas et al., 2012; Raggi et al., 2011); (3) patients who are working or studying will present a lesser degree of disability than those who are not working (De Wolf et al., 2012; Garin et al., 2010); and (4) patients in euthymic phase will show a lesser degree of disability compared to those who are not in said phase of the disease (Bonnín et al., 2012; Garin et al., 2010).

2. Methods 2.1. Sample description Patients diagnosed with bipolar I disorder according to DSM-IVTR criteria (American Psychiatric Association, 2000a) were enrolled in this study from 2007 to 2009 throughout 40 outpatient psychiatric clinics across Spain. A detailed explanation of the study design and sample recruitment has been reported elsewhere (Gómez-Benito et al., 2013, 2014). Briefly, a multicenter observational study was conducted to assess the psychometric properties of several measures, including cognitive functioning and disability. Patients were required to be over 18 and under 55 years of age and give their written consent to participate. Those with severe or unstable medical or neurological problems and those who were illiterate, had other primary psychiatric disorders including major depression or were already participating in a clinical trial were excluded from the study. Sampling was consecutive among the patients who were on the daily list of psychiatrists and met the enrolment criteria. Participating centers were selected at random and weighted by the regional population distribution in the country. The study was approved by the Ethics Committee of the University of Barcelona. A total of 291 patients with bipolar disorder (42.6% male) were included in the study, with a mean age of 40.43 (SD¼9.38). Table 1 lists the main sociodemographic characteristics of the sample. The average duration of illness was 11.92 (SD¼ 7.84; Range¼ 0.1–35) years, and they had experienced an average of 0.22 (SD¼ 0.56; Range¼ 0–4) manic episodes, 0.25 (SD¼0.51; Range¼0–3) depressive episodes and 1 The study by Garin et al. (2010) analyses how the WHODAS 2.0 works in different conditions, including bipolar disorder, but the scale’s psychometric properties are not presented separately for each condition, so there are no specific results for bipolar disorder other than the general descriptive data for the WHODAS 2.0 domain scores.

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0.13 (SD¼ 0.38; Range¼0–2) hospital admissions. Some patients presented another disorder (n¼36, 12.4%), mostly hypertension (n¼ 5), generalized anxiety (n¼5), or hypothyroidism (n¼4). At the time of assessment, patients were on lithium (n¼43; 14.8%), lithium plus one antipsychotic (n¼88; 30.2%), lithium plus two or more antipsychotics (n¼ 8; 2.8%), one antipsychotic (n¼101; 34.7%), or two or more antipsychotics (n¼ 19; 6.5%. Thirty-two patients were free of lithium and antipsychotics. 2.2. Instruments The WHODAS 2.0 (World Health Organization, 2000; Spanish version by Vázquez-Barquero et al., 2000) is an ICF-based multidimensional instrument developed for measuring disability. The complete version of the instrument contains 36 items that examine difficulties due to a health condition in six domains: cognition— understanding and communicating (6 items); mobility—moving and getting around (5 items); self-care—attending to one’s hygiene, dressing, eating and staying alone (4 items); getting along—interacting with others (5 items); life activities—domestic responsibilities, leisure, work and school (8 items); and participation—joining in community activities, participating in society (8 items). Patients have to answer questions regarding how much difficulty they have had in the last 30 days. Items are scored using a 5-point scale ranging from 1¼none to 5¼ extreme/cannot do. Scores may vary from 0 to 100, with higher scores reflecting greater disability. There are self-, interviewer- and proxy-administered versions, each of which are available in long (36 items) and screening (12 items) formats. There is also a hybrid form of both versions (12þ 24 items) that may only be administered by interview or computer-adaptive testing. In this study, we used the 36-item interviewer-administered version. Table 1 Sociodemographic characteristics of the sample. Variable

N

%

124 100 17 4 43

42.6 34.4 5.8 1.4 14.8

3 94 113 77 4

1.0 32.3 38.8 26.5 1.4

a

Marital status Single Married Living with couple Widow(er) Separated or divorced Educational level Functional illiterate Primary education Secondary education University education Other a

Variable Living arrangement Original family Own family Friends Sheltered housing Alone Other Employment status Employed (or student) Unemployed (or retired) Disability

N

%

120 125 5 1 36 4

41.2 43.0 1.7 0.3 12.4 1.4

102 110 79

35.1 37.8 27.1

Overall percentage is not 100% due to missing data.

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In addition to the WHODAS 2.0, patients completed a comprehensive assessment battery including measures on psychopathology, functionality and quality of life. All these measures are described in the next paragraphs and have been proved to function adequately from a psychometric perspective. In addition, the Spanish versions of these scales have been previously used in patients with bipolar disorder, all of them in Spanish studies except the EQ-5D in Venezuelan subjects with a bipolar disorder. Table 2 shows the distribution of scores and the respective internal consistency indices found in this study. The Young Mania Rating Scale (YMRS; Young et al., 1978; Spanish version by Colom et al., 2002) and the Hamilton Rating Scale for Depression (HAM-D; Hamilton, 1960, 1967; Spanish version by Ramos-Brieva and Cordero Villafáfila, 1986) were administered to assess manic and depressive symptoms. The YMRS is an 11-item clinician-rated scale designed to assess severity of manic symptoms. Administration time is 10–20 min. The instrument is widely used in both clinical and research settings. Information for assigning scores is gained from the patient’s subjective reported symptoms over the previous 48 h and from clinical observation during the interview. The scale is appropriate for assessing both baseline severity of manic symptoms and response to treatment in patients with bipolar disorder type I and II. The HAM-D is a clinician-administered depression assessment scale. The 17 items pertain to symptoms of depression experienced over the past week and are rated on either a 5-point (0¼absent to 4¼ very severe) or a 3-point (0¼ absent to 2¼definite) scale. The Clinical Global Impression-Severity scale (CGI-S; Guy, 1976; Spanish validation by Haro et al., 2003) was applied to rate the severity of the patient’s illness. The CGI-S is a 7-point scale that requires the clinician to rate the severity of the patient’s illness at the time of assessment, based on the clinician’s past experience with patients who have the same diagnosis. The rating system is 1¼normal, not at all ill; 2¼borderline mentally ill; 3¼ mildly ill; 4¼moderately ill; 5¼ markedly ill; 6¼severely ill; or 7¼ among the most severely ill patients. The Social and Occupational Functioning Assessment Scale (SOFAS, American Psychiatric Association, 1994; Spanish version by the American Psychiatric Association, 2000b) is an instrument that assesses the social, occupational, and psychological functioning of adults on a numerical scale ranging from 100 (excellent functioning) to 0 (persistent impaired functioning). Participants were asked to answer in relation to the worst week in the past month. Lastly, the EuroQoL-5D questionnaire (EQ-5D; The EuroQol Group, 1990; Rabin and de Charro, 2001; Spanish version by Badia et al., 1999) was applied to consider quality of life in relation to health status. The EQ-5D is a generic health-related quality of life instrument that consists of a vertical line (like a thermometer) with two ends that represent the best and worst imaginable health

Table 2 Distribution of scores and reliability coefficients for the WHODAS 2.0 domains and the other measures administered. Scale/domain

Mean

SD

Observed range

Missing (%)

Floor (%)

Ceiling (%)

Cronbach’s alpha

WHODAS 2.0 Cognition Mobility Self-care Getting along Life activities Participation YMRS HAM-D CGI-S SOFAS EQ-5D

16.89 8.30 3.93 19.72 21.23 19.85 3.27 4.80 2.69 71.26 70.88

18.83 16.41 9.54 22.96 25.52 21.12 5.31 5.16 1.35 15.47 18.50

0–85 0–81 0–50 0–100 0–100 0–100 0–32 0–31 1–6 25–98 12–100

0.0 0.3 0.3 2.4 2.4 2.7 1.0 3.1 0.7 3.1 2.7

33.0 67.4 78.7 36.7 46.7 32.0 41.0 19.1 28.4 0.0 0.0

0.0 0.0 0.0 0.3 0.7 0.3 0.0 0.0 0.0 0.0 1.4

.88 .84 .73 .85 .92 .90 .87 .84 – – –

WHODAS 2.0: World Health Organization Disability Assessment Schedule 2.0; YMRS: Young Mania Rating Scale; HAM-D: Hamilton Rating Scale for Depression; CGI-S: Clinical Global Impression-Severity; SOFAS: Social and Occupational Functioning Assessment Scale; EQ-5D: EuroQoL-5D questionnaire.

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statuses and correspond to a score of 100 or 0, respectively. Patients have to mark the score that best represents their health status today. 2.3. Statistical analysis Analyses were centered on providing evidence on the validity and utility of the WHODAS 2.0. The distribution of scores on the scale was characterized in terms of percentage of missing data, mean score and standard deviation, and percentage of subjects with minimum or maximum possible score (floor effect and ceiling effect, respectively). A confirmatory factor analysis (CFA) was carried out to assess the dimensional structure of the WHODAS 2.0 according to the six domains established by the authors of the scale. Parameters were estimated by the robust maximum likelihood method, by first obtaining the covariance matrices and asymptotic covariance matrices with the Prelis program. According to MacCallum and Austin (2000), several measures of model fit were considered: (a) χ2 goodness of fit statistic; (b) the ratio of χ2/df (degrees of freedom); (c) root mean square error of approximation (RMSEA) and its relative confidence interval; (d) non-normed fit index (NNFI); (e) comparative fit index (CFI); and (f) Akaike information criterion (AIC). According to authors such as Hu and Bentler (1999) and Kaplan (2000), goodness-of-fit indicators were considered as: χ2/df ratio o2; CFI Z.90; NNFI Z.90; and RMSEA r.05. Regarding the AIC, values close to zero reflect a good fit, and between two AIC values, the lower one reflects the model with the better fit. Internal consistency was studied by obtaining Cronbach’s alpha coefficient of each WHODAS 2.0 subscale. The relationship between the WHODAS 2.0 scores and the measures of clinical symptoms, functionality and quality of life were studied using the Pearson product-moment correlation coefficient. The Bonferroni correction for multiple comparisons was applied and statistical significance was set at po.002 (.05/30¼.002). Furthermore, the capacity of the WHODAS 2.0 to differentiate between known-groups was studied. The groups were defined using two different criteria: (a) patients were classified as euthymic or non-euthymic according to the intensity of clinical symptoms: euthymic when they obtained a score o7 on the YMRS and o8 on the HAM-D scale; (b) patients were grouped as workers or students and non-workers according to their work situation at the time of assessment. In both cases, the magnitude of the differences between WHODAS 2.0 scores was obtained by calculating Cohen’s d, that is by subtracting the mean scores in both groups and dividing them by the pooled standard deviation. Confirmatory factor analysis was carried out using the Prelis v. 2.50 and LISREL v. 8.8 programs, while the PASW version 17.9 statistics package was used for the rest of the analyses. Computations were performed on all available data.

88.9% of the subjects with missing values had less than 5 missing values. Table 2 shows the statistics that enable the WHODAS 2.0 to be characterized. In terms of missing values in each domain, the Participation domain had the highest percentage of missing data, specifically 2.7%, although all of them are low enough to provide data in favor of WHODAS 2.0 feasibility. It should be highlighted that the mean domain scores are generally quite low, especially in the Getting along and Self-care subscales, to the extent that the floor effects in both domains were considerable. There were no noteworthy ceiling effects in any subscale. 3.2. Dimensional structure To contrast the first of the hypotheses on validity, we tested the structure of the six correlated domains proposed by the test authors using CFA. We contrasted said model with alternative models, such as that suggested by Üstün et al. (2010) which specifies a second-order factor underlying the six primary factors; and the model suggested by Chwastiak and Von Korff (2003) that consists of specifying a structure with two second-order factors, the first comprising the first three domains and the second spanning the last three. Table 3 presents the goodness-of-fit rates obtained by the three models. It can be seen that they all have very good goodness-of-fit (χ2/df less than the cutoff of 2; RMSEA index less than .05, without the confidence interval containing said value; NNFI and CFI indices much greater than .90). However, model 1 is the model that best represents the reality of the data, due both to its lower AIC value and its slight superiority in the values reached by all the fit indices. Saturations of the selected model 1 are statistically significant and of high magnitude (ranging from .54 to .68), revealing that they are all good indicators of the corresponding domain. The saturations of the other two models are very similar (there are only centesimal changes), which shows the stability of the estimates obtained. 3.3. Internal consistency As shown in Table 2, following assessment criteria by Kline (2000), the alpha coefficients obtained in each WHODAS 2.0 subscale show that the instrument applied to a sample of patients with bipolar disorder presents suitable internal consistency. Specifically, the alpha values range between .73 for the Self-care domain and .92 for Life activities. It should also be highlighted that the Self-care domain is the only domain that would not fall into the category of excellence in terms of reliability, and eliminating the item with the lowest item-test correlation would not involve a substantial increase in internal subscale consistency. The Cronbach’s alpha of the total scale was .96. 3.4. Relations with other variables

3. Results 3.1. Score distribution There were 27 (9.8%) patients who did not respond to one or more of the items, with a range of 1–9 items unanswered, although

With the aim of testing hypothesis 2, we computed the correlations between WHODAS 2.0 subscales and the rest of the scales used to assess clinical symptoms, functionality and quality of life. Table 4 shows the coefficients obtained, which support the suggested hypothesis that postulates the existence of a relationship

Table 3 Goodness of fit statistics for the three models compared. Model

χ2

χ2/df

RMSEA

90% CI

NNFI

CFI

AIC

Six first order factors Six factors loading on a higher-order factor Two higher-order factors with three domains each

617.89 740.73 740.51

1.376 1.617 1.620

.036 .046 .046

.029–.043 .040–.052 .040–.052

.98 .98 .98

.99 .98 .98

775.89 880.73 882.51

χ2 ¼Satorra–Bentler scaled chi-square; df¼ degrees of freedom; RMSEA ¼ root mean square error of approximation; CI ¼ confidence interval; NNFI ¼non-normed fit index; CFI¼ comparative fit index; AIC¼ Akaike information criterion.

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Table 4 Correlations between the WHODAS 2.0 domains and other related measures. Domain

YMRS

HAM-D

CGI-S

SOFAS

EQ-5D

Cognition Mobility Self-care Getting along Life activities Participation

.250n .065 .121 .189n .255n .309n

.597n .422n .448n .580n .537n .637n

.610n .396n .341n .552n .551n .629n

 .585n  .401n  .389n  .539n  .498n  .599n

 .427n  .394n  .396n  .391n  .400n  .473n

n po .002; YMRS: Young Mania Rating Scale; HAM-D: Hamilton Rating Scale for Depression; CGI: Clinical Global Impression-Severity; SOFAS: Social and Occupational Functioning Assessment Scale; EQ-5D: EuroQoL-5D questionnaire.

between these variables, in most cases with medium or large correlations following Cohen’s criteria (Cohen, 1988). The measure that, as a set, presents the most noteworthy correlations with WHODAS 2.0 is the HAM-D, with values ranging between .422 for Mobility and .637 for Participation. The WHODAS 2.0 domain that presents the highest coefficients of correlation in general is Participation, with correlations ranging between .309 for YMRS and .637 with HAM-D. Moderate-to-high correlations were also obtained with both the CGI (values between .341 for Self-care and .629 for Participation) and the SOFAS (correlations between  .389 for Selfcare and  .599 for Participation), and, to a lesser extent, with the health-related quality of life scale, obtaining correlations between .391 for Getting along and .473 for Participation. Very low correlations were observed with the YMRS scale, with the correlations being practically null in some cases. In the evaluation of the capacity of WHODAS 2.0 to differentiate between known-groups, it should be noted that 102 patients from the total sample (35.1%) were working or studying at the time of assessment, while 189 patients (64.9%) were not; also, among worker or student patients, 85.6% were euthymic (YMRS total o7 and HAMD o8), whereas in the case of non-workers, 69.7% were euthymic (χ2(1)¼8.334, p¼.004). In the evaluation of hypothesis 3, by comparing the WHODAS 2.0 scores between the groups defined according to working situation (see Fig. 1a), we found that patients who were working or studying at the time of the evaluation had lower scores overall (d¼0.65) and in all the domains, indicating a lower degree of disability in this patient group. According to Cohen’s criteria (Cohen, 1988), the effect sizes were mild to moderate with values ranging between d¼0.35 for Self-care and d¼ 0.64 for Participation. Along the same lines, when contrasting hypothesis 4, comparing the scores according to clinical symptoms (see Fig. 1b), and patients in the euthymic phase presented lower scores overall (d¼ 1.83) and in each and every one of the WHODAS 2.0 domains, suggesting a lower degree of disability than in the patients who did not meet this criterion. The effect size of the Participation subscale was especially noteworthy, suggesting that the magnitude of difference in these scores is greater than 1.5 standard deviations.

4. Discussion Over the course of this study, new reliable and valid evidence has been presented for the WHODAS 2.0 scale in the evaluation of disability in patients diagnosed with bipolar disorder, and the psychometric properties of the 36-item version were applied to this patient type for the first time. On the one hand, the reliability analysis has shown that the different domains and the total score of the scale present satisfactory internal consistency and, on the other, the sixdomain dimensional structure and the relationship of the WHODAS 2.0 with other clinical measures of functionality and quality of life lead to the conclusion that it is a valid instrument when used in patients with bipolar I disorder. Regarding the dimensionality of the WHODAS

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2.0, the results support extending the original structure of the six domains to bipolar patients. However, it should be noted that the three tested models, all with excellent fit indices, are highly viable, supporting the fact that not only is the use of the different WHODAS 2.0 domain scores validated, but so is the use of the instrument’s total score as an overall measure of disability, as proposed by Üstün et al. (2010), and even of the two dimensions of disability (Activity limitations and Participation) proposed by Chwastiak and Von Korff (2003) in the framework of the ICF model. In all, the good results found with the complete version of the WHODAS 2.0 lead us to hypothesize that the reduced 12-item version may also be a plausible candidate for patients with bipolar disorder, as has been demonstrated in other diseases (Luciano et al., 2010a, 2010b, 2010c; Perini et al., 2006; Sousa et al., 2010). Additionally, as there is little variability in the scores and the floor effects observed in some of the WHODAS 2.0 domains, this seems to suggest that the scale may present difficulties for discriminating between the degrees of disability of patients who are close to adequate functionality. Nevertheless, if we look at the overall percentage of patients in euthymic phase (68.0%), we can conclude that those patients affected by more severe symptoms may possibly be underrepresented in our sample. This might also explain the low correlations found between WHODAS 2.0 and YMRS; probably due to the predominance of euthymic patients, range and variability of scores are restricted, thus limiting the values of correlation coefficients. If a greater number of non-euthymic patients were added, the floor effects of some of the WHODAS scales would surely decrease considerably. The results found by Chopra et al. (2004) must be added to this argument; they determined that problems with social withdrawal and self-care were under-reported in patients with schizophrenia, which could be explained by a certain lack of disease awareness. In the case of the Self-care domain, and similarly to this study, the studies by Garin et al. (2010) in patients with chronic disease and by Pösl et al. (2007) in patients with back pain and depression found that a considerable percentage of patients obtained the best score possible. Nevertheless, it seems that disability in patients with bipolar disorder is restricted to Cognition, Getting along, Life activities, and Participation. These results are in line with other studies (Rosa et al., 2008) that assess disability in bipolar patients using other multidimensional measures such as the Functioning Assessment Short Test (Rosa et al., 2007). In sum, the Spanish version of the 36-item WHODAS 2.0 has suitable psychometric properties in terms of reliability and validity when applied to patients with bipolar disorder. It must be stressed that both the WHODAS 2.0 and the ICF Checklists were created with the aim of facilitating the assessment of functionality and disability in the context of the ICF classification system, but these two instruments are generic in the sense that they may be used to assess functionality and disability in any disease, not just bipolar disorder. Notwithstanding, having more specific and concrete information on the disorder under study is sometimes necessary. In this context, the WHO is working on the creation of the so-called Comprehensive and Brief ICF Core Sets for several diseases, which in the case of bipolar disorder consists of 38 categories for the complete version and 19 for its short version (Ayuso-Mateos, et al., 2013). As a result, observing how this instrument behaves in relation to the specific ICF Core Set for bipolar disorder would provide new evidence in favor of the good functioning of the WHODAS 2.0 scale for bipolar disorder. This new study would involve comparing the conclusions extracted from the WHODAS 2.0 with those based on results from the ICF Core Set.

5. Limitations Our study is not without its limitations. The first, as we pointed out, refers to the sample composition, in which the percentage of euthymic patients is considerable. However, the assessment of euthymic patients

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Fig. 1. WHODAS 2.0 scores (mean, 95% confidence intervals and effect size d in relation to employment status (a) and clinical status (b)). Footnote: C: cognition; M: mobility; S: self-care; Ga: getting along; La: life activities (LaH: life activities, household); P: participation.

is less influenced by mood. Indeed, subjective measures such as the WHODAS 2.0 may be influenced by the patients’ mood at the time of the evaluation (Dean et al., 2004), and therefore the scores obtained would present a certain degree of bias and the inferences made from these scores regarding the degree of patient disability would therefore be under question. Thus, the most recent research is aimed at the search for objective measures such as performance-based assessment of functional capacity and third-party ratings of functional behavior (Rosa et al., 2007; Bowie et al., 2010; Vieta, 2014). Lastly, some

important psychometric properties have not been studied, such as WHODAS 2.0 score stability and sensitivity to change.

6. Conclusion Regardless of these limitations, WHODAS 2.0 is a useful and adequate tool to assess disability and functionality from the perspective of the patient with bipolar disorder. If health professionals

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have at their disposal patient information regarding the most limiting aspects of daily living and how greatly the patients are affected, treatments such as functional remediation (Torrent et al., 2013; Solé et al., 2014) can be focused precisely on improving these issues and, as a result, increase the quality of life of patients, their family members and society in general.

Role of funding source Javier Rejas who is employee of one of the funding sources of this work participated in data interpretation and drafting of manuscript.

Conflict of interest The statistical analysis of this work was funded by Pfizer, S.L.U. Data collection in the original study source for the analysis included here was funded by Pfizer, SLU, and also received grants from Ministerio de Economía y Competitividad (PSI2012-32275), Instituto de Salud Carlos III, CIBERSAM and the Ministerio de Sanidad y Consumo: Plan Nacional de Drogas (2008/I/30) and Gobierno de Navarra (GON 55/200). Editorial support was funded by project 2014SGR1139 (J. Gómez-Benito y G. Guilera) and 2014SGR398 (E. Vieta y A. Martínez-Arán) from Departament d’Universitats, Recerca i Societat de la Informació de la Generalitat de Catalunya. Grammatical review was carried out by NOVA Traduciones and was funded by Pfizer, SLU. Javier Rejas is employ of Pfizer, SLU. All other authors declare that they have no conflict of interest as a consequence of this work.

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