Journal of Clinical Epidemiology 68 (2015) 551e562

A brief form of the Perceived Social Support Questionnaire (F-SozU) was developed, validated, and standardized oßlea, Florian Rehbeina, Deborah F. Hellmanna, Markus Zengerb, S€ oren Kliema,*, Thomas M€ Elmar Br€ahlerb,c a Criminological Research Institute of Lower Saxony, L€utzerodestraße 9, 30161 Hannover, Germany Department of Medical Psychology and Medical Sociology, University of Leipzig, Ph.-Rosenthal-Str. 55, 04103 Leipzig, Germany c Department of Psychosomatic Medicine and Psychotherapy, University of Mainz, Untere Zahlbacher Str. 8, 55131 Mainz, Germany b

Accepted 3 November 2014; Published online 13 November 2014

Abstract Objectives: Development of a brief instrument (F-SozU K-6) for the measurement of perceived social support in epidemiologic contexts by shortening a well-established German questionnaire (F-SozU K-14). Study Design and Setting: The development of the F-SozU K-6 consisted of two phases; phase 1: the F-SozU K-14 was presented to a general population sample representative for the Federal Republic of Germany (N 5 2,007; age: 14e92 years). Six items for the short form were selected based on the maximization of coefficient alpha. Phase 2: the new short form (F-SozU K-6) was evaluated and standardized in an independent second population survey (N 5 2,508, age: 14e92 years). Results: The F-SozU K-6 showed very good reliability and excellent model fit indices for the one-dimensional factorial structure of the scale. Furthermore, strict measurement invariance was detected allowing unbiased comparison of means and correlation coefficients and path coefficients between both sexes across the full lifespan from adolescence (14e92 years). Well-established associations of perceived social support with depression and somatic symptoms could be replicated using the short form. Conclusion: The F-SozU K-6 presents a reliable, valid, and economical instrument to assess perceived social support and can thus be effectively applied within the frameworks of clinical epidemiologic studies or related areas. Ó 2015 Elsevier Inc. All rights reserved. Keywords: Perceived social support; Self-report questionnaire; Standardization; Social Support Questionnaire short form (F-SozU K-6); Measurement invariance; Psychometrics; Confirmatory Factor Analysis

1. Introduction In the field of clinical epidemiology, economizing selfassessment instruments seems of particular relevance. This is especially true for large population samples, with the necessity to assess a variety of relevant constructs and given space constraints due to reasons of costs and acceptance. One solution to this problem could be to include short forms of well-established instruments, which are highly correlated with their long versions. In the past, numerous

Conflict of interest: None. Funding: The study was authorized by the Ethics Committee of the Medical Faculty of the University of Leipzig (Az.: 050/13-03.05.2013). The study was financed by internal funds of the Department for Medical Psychology and Medical Sociology of the University Clinic of Leipzig. * Corresponding author. Tel.: þ49-(0)511-34836-70; fax: þ49-(0)51134836-10. E-mail address: [email protected] (S. Kliem). http://dx.doi.org/10.1016/j.jclinepi.2014.11.003 0895-4356/Ó 2015 Elsevier Inc. All rights reserved.

short forms assessing physical health or physical constraints [1e4] and psychopathology (eg, depression [5e7], anxiety [6,8], somatoform disorder [3,9], or posttraumatic stress symptoms [10,11]) have been either well established or recently developed. In addition to these clinically relevant measures, short forms of more general constructs are needed that possibly (1) maintain or induce pathology, (2) moderate or mediate the outcome of medical or psychotherapeutic interventions, or (3) could be seen as secondary outcome measures (eg, quality of life or global functioning). Decades of research have shown that perceived social support plays an essential role in preventing mental and physical illness [12e17]. Correspondingly, a current meta-analysis [12], which evaluated three major components of social relationships, shows that regarding mortality, the importance of the functional aspects of social relationship (ie, received and perceived social support) may be rated as comparable to other well-researched risk

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What is new? Key findings  Decades of research have shown that perceived social support plays an essential role in preventing mental and physical illness. In this study, the six-item brief social support questionnaire, F-SozU K-6, was developed and evaluated based on two independent surveys, representative of the general population of Germany.  The F-SozU K-6 showed very good reliability, and excellent model fit indices were detected for the one-dimensional factorial structure of the scale. What this adds to what was known?  The F-SozU K-6 provides an economical and reliable instrument for evaluating the degree of perceived social support.  Based on measurement invariance analyses, the F-SozU K-6 allows comparison of means and correlation coefficients, as well as path coefficients within structural equation models between both sexes across the full lifespan (14e92 years). What is the implication and what should change now?  The application of the F-SozU K-6 within the frameworks of clinical epidemiologic studies or related areas is supported.

factors, such as smoking or regular alcohol consumption, and even surpasses the importance of other risk factors, such as obesity or physical inactivity. Furthermore, social support can be awarded to have relevance in medical settings, for example, the development and progression of cardiovascular disease [18], compliance with medical regimens [19], and a decreased length of hospitalization [20]. 1.1. Measures of social support The importance of the concept of social support is also reflected in the number of measures developed for its assessment. However, available instruments for assessing perceived social support seem to be unsuited in the framework of clinicaleepidemiologic studies due to the number of items [eg, MSPSS (Multidimensional Scale of Perceived Social Support) [21], SPS (Social Provisions Scale) [22], DUFSS (Duke-UNC Functional Social Support Questionnaire) [23], ASSIS (Arizona Social Support Interview Schedule) [24], PSSS (Perceived Social Support Scale) [25], SSQ (Social Support Questionnaire) [26]]; low

validity or reliability [eg, short forms of the OSSS (Oslo Social Support Scale) [27,28], short form of the SPS [29]]; or elaborated scoring [NSSQ (Norbeck Social Support Questionnaire) [30], SSQ-6 [31]] or they have not been conceived [eg, mMOS-SS (modified Medical Outcomes Study Social Support Survey) [32], DUFSS-10 [33]] or even evaluated (DUFSS-8 [34], DUFSS-6 [35], NSSQ [30], SSQ-6 [31]) in the general population. 1.2. The German Social Support Questionnaire In German-speaking countries, the Social Support Questionnaire (F-SozU) by Fydrich et al. [36] is well accepted to assess general social support in the general population and in clinical trials. Since the 1980s, it is primarily used in research contexts in clinical psychology, psychotherapy, medical sociology, health psychology, and behavioral medicine [37]. Following Barrera [38], Heller and Swindle [39], and House [40], the authors conceptualize social support as perceived or anticipated support from the social network. This cognitive approach goes back to Cobb [41] and focuses on the assessment by the recipient of social support. Several studies have shown that in clinical and epidemiologic contexts, this perspective attains higher significance than formal or structural network characteristics. The FSozU assesses social support in the natural environment (general social support) that excludes help from health care professionals [37]. From an individual perspective, statements regarding perceived or anticipated social support are rated on a five-point Likert scale, ranging from 1 (does not apply) to 5 (exactly applicable). These statements cover generalized experiences rather that concrete situations. A long version with 54 items (S-54) [36,37] and a short version with 22 items (K-22) [37] cover three central characteristics of social support: practical and material (instrumental) support (being able to receive practical help with daily problems, for example, borrowing something, receiving practical advice, being relieved of tasks), emotional support (being liked and accepted by others, being able to show feelings, experiencing sympathy), and social integration (belonging to a circle of friends, undertaking ventures together, knowing people with similar interests). These dimensions can be interpreted as subscales and combined to a total score of general perceived social support. Although also containing items from all the three dimensions, another short version comprising 14 items (K-14) [37,42] focuses exclusively on general perceived social support, which in this instrument is not further differentiated. Hence, the authors suggest an unidimensional interpretation of a total score. Quality criteria of the F-SozU K-14 are overall convincing, showing high consistency of the instrument (a 5 0.94) and satisfactory selectivity between 0.55 and 0.76 [42]; a 1-week retest reliability of 0.96 is specified. All short forms were generated by selecting items based on psychometric properties [37].

S. Kliem et al. / Journal of Clinical Epidemiology 68 (2015) 551e562

Perceived social support as measured by the F-SozU has been shown to be associated with social competence, social insecurity, psychopathological symptoms as well as several social, and sociodemographic variables [eg, gender (higher values for woman), relationship status (higher values for being in a relationship), educational status (higher values for individuals with university degree)] in accordance with its theoretical framework and hence provides support for construct validity [37]. These relations could be replicated using the short forms [37].

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and providing German norms for clinicalepsychological instruments. Hence, in this study, detailed information of procedure and sample characteristics are only provided for phase 2 where the F-SozU K-6 was used, please refer to Fydrich et al. [42] for more details on the survey from phase 1.

3. Phase 1: development of the short form of the F-SozU 3.1. Method of phase 1

1.3. Aims of the study For use within the context of clinical epidemiology, it would be desirable to have an economical (ie, low completion and scoring time) instrument convincingly covering various areas of perceived social support that is still characterized by high reliability and validity. The goals of this study were hence to (1) develop a brief form for assessing social support (F-SozU K-6) based on the F-SozU K-14, using a representative community sample, and (2) subsequently examine its psychometric properties and standardize this brief form in a second representative population sample. To the best of our knowledge, to date, no shorter versions of the F-SozU than the F-SozU K-14 have been developed and validated.

2. General method 2.1. Overview The development of the brief form was carried out in two phases. Phase 1: In the first phase, the F-SozU K-14 was administered to a community sample. Based on the data collected in phase 1, the items were evaluated and the short form F-SozU K-6 was compiled. Phase 2: In a second general population survey, the newly developed brief form (F-SozU K-6) was administered and evaluated. Norms regarding age and gender were compiled. 2.2. Procedure The overall design of the two surveys was highly similar. Both surveys were conducted by the University of Leipzig and were carried out by the same contractor [an independent institute for opinion and social research (USUMA, Berlin)] using the same procedure. A final sample size of 2,500 participants was intended in both surveys. Aims of these annual surveys were to (a) assess prevalence rates of a variety of relevant physical or mental disorders and related risk behaviors (descriptive epidemiology), (b) examine causes and conditions of these disorders (analytic epidemiology), and (c) analyze psychometric properties

3.1.1. Study design and participants The development of the brief form was carried out based on data from a representative sample of the Federal Republic of Germany from a 2003 survey by the University of Leipzig [N 5 2,007 aged between 14 and 92 years; for a more detailed description, see 42] and authorized by the Ethics Committee of the Medical Faculty of the University of Leipzig. 3.1.2. Statistical analyses Criteria for the shortened scale were a very good coefficient alpha value, unidimensionality of the instrument (necessary to calculate a total score), and a small number of items (max. six items) to provide an economic measurement of perceived social support. The shortened scale should preferably contain the same number of items for each of the three dimensions originally postulated. Original wording was maintained for all items. We used Hayes’ alphamax macro [43] to establish an optimal combinations of items regarding coefficient alpha (the alphamax algorithm maximizes coefficient alpha over every possible combination of items). Subsequently, confirmatory factor analysis (CFA) was conducted to compare potential abbreviated item sets. The CFA estimation followed the procedure mentioned in the method section. 3.2. Results of phase 1 Internal consistency as expressed by Cronbach’s alpha was a 5 0.94. The mean sum score of the F-SozU K-14 was 3.97 (standard deviation (SD) 5 0.97), and the full range from 1 to 5 points was exploited. To allow for comparison with the short form, Table 1 lists the item characteristics of the F-SozU K-14.

4. Phase 2: psychometric evaluation of short form F-SozU K-6 The newly created brief questionnaire (F-SozU K-6) was subsequently analyzed based on an independent survey that was again representative of the Federal Republic of Germany with regard to its psychometric parameters. The

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Table 1. Mean (M), SD, item difficulty (Pi), corrected itemetotal correlation (rit), and group differences for the F-SozU K-14 items and total scores Item English

Total German

I can easily find someone Ich finde ohne weiteres who can look after my jemanden, der sich um home when I’m not there. meine Wohnung €mmert, wenn ich mal ku nicht da bin. There are people who Es gibt Menschen, die mich accept me the way I am ohne Einschr€ankung so without reservations. nehmen wie ich bin. I receive a lot of Ich erfahre von anderen viel understanding and Verst€andnis und security from others. Geborgenheit. There is someone very close Ich habe einen sehr to me whose help I can vertrauten Menschen, always count on. mit dessen Hilfe ich immer rechnen kann. If I need to, I can borrow Bei Bedarf kann ich mir something from friends ohne Probleme bei or neighbors without any Freunden oder Nachbarn problems. etwas ausleihen. I have friends/relatives who Ich habe Freunde/ will definitively take time Angeh€orige, die sich auf to listen if I need jeden Fall Zeit nehmen someone to talk to. und gut zuh€oren, wenn ich mich aussprechen m€ochte. I know several people with Ich kenne mehrere whom I like to do things. Menschen, mit denen ich gerne etwas unternehme. I have friends/relatives who Ich habe Freunde/ sometimes simply give Angeh€orige, die mich me a hug. einfach mal umarmen. When I am sick, I can ask Wenn ich krank bin, kann ich ohne Z€ogern Freunde/ friends/relatives to Angeh€orige bitten, handle important things € r mich wichtige Dinge fu for me without hesitation. zu erledigen. If I’m very depressed, I Wenn ich mal sehr € ckt bin, weiß ich, know who I can turn to. bedru zu wem ich damit ohne weiteres gehen kann. There are people who share Es gibt Menschen, die both joy and sorrow with Freude und Leid mit mir me. teilen. I have some friends/ Bei manchen Freunden/ relatives with whom I can Angeh€origen kann ich be quite playful. auch mal ganz ausgelassen sein. There is someone close to Ich habe einen vertrauten me in whose presence I Menschen, in dessen feel comfortable without N€ahe ich mich ohne any reservations. Einschr€ankung wohl €hle. fu There is a group of people Es gibt eine Gruppe von (friends, clique) that I Menschen (Freundeskreis, belong to and whom I Clique), zu der ich geh€ore meet often. und mit der ich mich h€aufig treffe. F-SozU K-14 mean score

M

SD

Men Pi

rit

M

SD

Group difference

Women Pi

rit

M

SD

Pi

rit

t

4.08 0.91 77 0.65 4.03 0.97 76 0.66 4.12 0.87

78 0.65 2.46*

4.12 0.82 78 0.71 4.08 0.82 77 0.69 4.15 0.82

79 0.72 2.31*

3.91 0.88 73 0.73 3.85 0.91 71 0.74 3.96 0.86

74 0.71 3.10*

4.18 0.89 80 0.73 4.14 0.91 79 0.74 4.22 0.88

81 0.73 2.12*

4.06 0.87 77 0.67 4.00 0.90 75 0.67 4.10 0.85

78 0.68 3.07*

3.93 0.86 73 0.76 3.87 0.87 72 0.73 3.99 0.85

75 0.77 3.48

3.95 0.91 74 0.71 3.93 0.88 73 0.69 3.97 0.93

74 0.73 1.13

3.75 1.03 67 0.69 3.60 1.06 65 0.68 3.88 1.00

72 0.70 6.70**

4.03 0.86 76 0.71 3.96 0.88 74 0.71 4.08 0.84

77 0.71 3.52**

3.97 0.90 74 0.76 3.86 0.92 72 0.75 4.06 0.87

77 0.77 5.58**

3.97 0.90 74 0.73 3.89 0.95 72 0.71 4.04 0.85

76 0.75 4.09**

3.96 0.91 74 0.71 3.92 0.90 73 0.71 4.00 0.92

75 0.70 2.34*

4.09 0.91 77 0.71 4.05 0.93 76 0.73 4.12 0.893 78 0.70 1.99*

3.61 1.10 65 0.55 3.63 1.07 66 0.57 3.59 1.13

65 0.54

3.97 0.68 d

d

d

3.91 0.69 d

d

4.02 0.67

d

1.05

3.86**

Abbreviation: SD, standard deviation. *P ! 0.05, **P ! 0.001. WHO-conform forwardebackward translation from German to English independently carried out by (in each case) two native speakers of the target language. Discrepancies were discussed in an expert panel with the result of a consensual solution.

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representative sample of this survey furthermore served as a norming group. 4.1. Method of phase 2 4.1.1. Study design and participants Data collection took place between April and June 2013. Sampling was conducted using a threefold random selection procedure: First, 258 sample points, representing different nonoverlapping inhabited areas in Germany, were randomly selected [44] from a German community inventory stratified according to the BIK Aschpurwis þ Behrens GmbH (BIK) classification system. The BIK is measuring the grade of urbanization and the geographic distribution [45]. Second, target households were selected randomly through the random route procedure with a specified starting address. Trained interviewers (k 5 198) were provided with a concrete street and a corresponding starting house number. Beginning with this address, every third household on the respective street was identified and contacted with the aim of conducting an interview. For this purpose, the addresses that had been identified were entered into an address list. Third, the random selection of the target person in the households was done with the help of a Kish selection grid to determine the target person. Before the target person was randomly selected, the interviewer checked criteria for inclusion (age  14 years and sufficient ability to understand written German language) for every potential participant. After giving full information on the study and data security, informed consent was obtained. Following a structured sociodemographic interview, participants completed self-report questionnaires on physical and psychological symptoms in the presence of (but without any interference from) the interviewer. The interviews were conducted at the participants’ homes. Reasons for nonparticipation and corresponding figures can be obtained from Fig. 1. At the institute, interviews and questionnaires were checked for completeness. Before data entry, the correct filter procedure was checked by an encoder, and if the circumstances were ambiguous, they were immediately corrected. After having been recorded, the data were checked in a second step based on the original questionnaire and, if necessary, corrected. Interviewers were controlled by sending prestamped postcards to the participants (37%, randomly chosen). About 53% of the postcards were returned; all of them confirmed proper conduct of the interview. The initial sample consisted of 4,360 persons, of which 2,508 (57.5%) participated in the full study. All procedures were authorized by the Ethics Committee of the Medical Faculty of the University of Leipzig. 4.1.2. Measures 4.1.2.1. Demographic questionnaire. Age, gender, family characteristics, student and employment status, and household income were surveyed. Based on the method of the research alliances within rehabilitation science, a social

Fig. 1. Flowchart of sampling procedure and reasons for nonparticipation (phase 2).

stratification index was created according to the following scores: school education (1: no certificate, secondary school; 2: high school, technical college; 3: university

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entrance diploma), lifetime professional status (1: laborer; 2: clerical worker, public servant; 3: freelancer), household income (1: !V1,250; 2: V1,250eV2,000; 3: OV2,000). 4.1.2.2. The Patient Health Questionnaire 2, German version. The Patient Health Questionnaire (PHQ-2) [46] is a two-item self-administered version of the PRIME-MD [47], a diagnostic instrument for common mental disorders. The PHQ-2 constitutes a depression module, which scores the two DSM-5 main criteria for major depression from 0 (not at all) to 3 (nearly every day). PHQ-2 sum scores range from 0 to 6, whereas higher values indicate higher burden of depression. In the present study, the German version of the PHQ-2 [48] was applied. The translation of the German version followed state-of-the-art procedures in cross-cultural assessment [49]. In a recent population-based study [6] and in the present study, the PHQ-2 reached high internal consistency (a 5 0.75; study at hand: a 5 0.80). 4.1.2.3. The Giessen Subjective Complaints List, German version. To assess somatic symptom strain, we used the short form of the Giessen Subjective Complaints List (Gießener Beschwerdebogen GBB-8; [50]). This inventory comprises eight items: for example, stomach ache, back pain, headaches, feeling tired, trouble sleeping, and dizziness. Each symptom is rated on a Likert scale from 1 (never) to 5 (always). GBB-8 sum scores range from 8 to 40, whereas higher values indicate higher somatic burden. In the study at hand, the GBB-8 reached a high internal consistency, a 5 0.89. 4.1.2.4. The Generalized Anxiety Disorder Scale-2, German version. In the Generalized Anxiety Disorder Scale -2 (GAD-2; [51,52]), two main symptoms of generalized anxiety disorder are assessed within the last 2 weeks using two questions on a four-point scale from 0 (not at all) to 3 (almost every day). GAD-2 sum scores range from 0 to 6, whereas higher values indicate higher burden of generalized anxiety. In the present study, the German version of the GAD-2 [6] was applied. The translation of the German version followed state-of-the-art procedures in cross-cultural assessment [49]. The GAD-2 showed high internal consistency (a 5 0.82; study at hand: a 5 0.79) in the general population [6]. 4.1.3. Statistical analyses Internal consistency of the F-SozU K-6 is reported as coefficient a. To determine selectivity, the correlation of the respective item with the sum of all other items was computed (itemerest correlations). Item difficulty coefficients were calculated as quotients of the sum of the item values that were obtained and the sum of the maximum achievable item values, multiplied by 100. We applied chained equation modeling [53] using the following variables: gender, age, monthly net income, educational status, and partnership

status to estimate missing data (proportion of missing values of analyzed items: 0.1  0.4%). To avoid nonexisting item values, the estimated values (^y) were corrected by predictive mean matching (ie, the observed values closest to the predicted value were chosen). We used the R package mice [54] for this analysis. To replicate well-established associations and hence provide evidence of validity of the F-SozU K-6, correlation coefficients with the PHQ-2 depression inventory, the GAD-2 anxiety inventory, and an inventory for somatic symptom strain, the GBB-8, were calculated. Based on the results of earlier surveys, the following hypotheses were formulated: (1) depression level should be higher in individuals with lower perceived social support scores [55,56], (2) anxiety level should be higher in individuals with lower perceived social support [55,56], and (3) somatic symptom strain should be higher in individuals with lower perceived social support [12]. We examined a simple general factor model with all items loading on one factor using CFA. This model allows for summarizing the item scores to a total score. Because of significant deviations from a multivariate normal distribution, the robust maximum likelihood estimation with a mean-adjusted chi-square test statistic (SatorraeBentler c2) was applied, which has been shown to be robust to the violation of normality [57]. Because inconsistent observations in surveys (eg, due to a sloppy answering style) can bias statistical results and distort conclusions [58], we conducted multivariate outlier detection. We used the newly developed item pairebased outlier score for rating scales (Gþ; [59]), which is defined as the number of weighted Guttman errors [60] to determine outlier scores. Gþ represents the degree to which a respondent is more favorable toward less popular items and is most useful for one-dimensional scales [59]. The outlier scores were then classified as discordant or not discordant using Tukey’s boxplot [61] for outlier detection. To evaluate goodness of fit of the relevant model, we considered four different criteria. Although the standardized root mean square residual (SRMR), root mean square error of approximation (RMSEA), and 90% confidence interval assess absolute model fit, the two additionally calculated criteria [Comparative Fit Index (CFI) and Tucker Lewis Index (TLI)] are measures of relative model fit, compared with the ‘‘null’’ model. RMSEA and SRMR values !0.050 represent a close fit, values between 0.050 and 0.080 represent a reasonably close fit, and values O0.080 represent an unacceptable model [62,63]. Regarding CFI and TLI, Hu and Bentler [63] suggested a CFI and TLI O0.900 for an adequate fit and a CFI and TLI O 0.950 for a good model fit. Furthermore, we conducted several measurement invariance tests across gender (group 1 5 men; group 2 5 women), age [group 1 ! 51 years (median split)  group 2], and gender  age interaction (group 1 women and !51 years; group 2 women and 51 years; group 3 men and !51 years; group 4 men and

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51 years). Measurement invariance tests were performed using the sequential strategy discussed by Meredith and Teresi [64]. First, we tested a configural invariance model. Configural invariance refers to the equivalence of the factorial structure. It is given if the analyzed constructs show the same dimensionality and, additionally, the observed variables are correlated with the same latent constructs in both groups. Configural invariance is a necessary, but not sufficient, condition to expect an unbiased comparison of measurements between groups. Second, we tested the weak invariance model by constraining the estimated factor loadings to be equal across groups. If empirical support for weak invariance is provided, it allows for comparing structural relationships [eg, correlation coefficients, structural (path) coefficients] between latent constructs in groups. Third, the strong invariance model was tested by constraining both intercepts and loadings to be equal across groups. This level of invariance enables the comparison of means of the latent construct between groups. Finally, we tested the strict invariance model by constraining the loadings, intercepts, and item error variances to be equal across groups. Different residual variances in groups can have two possible consequences. On one hand, it can lead to different reliabilities of indices

557

in those groups. On the other hand, it can affect decisions in screening processes that depend on the expression of a construct, resulting in different error rates (ie, sensitivity, specificity) for different groups [65]. As recommended by Chen [66], CFI differences with a cutoff value of DCFI O 0.01 were used for testing the different stages of measurement invariance. Data analysis was carried out with the R (R Core Team, 2013, Vienna, Austria) packages lavaan [67] and mice [54]. 4.2. Results 4.2.1. Sample characteristics Participants’ mean age was M 5 49.67 years (SD 5 18.30) with a range of 14e92 years; n 5 96 (3.8%) participants were not German regarding nationality. Further sample details can be found in Table 2. 4.2.2. Item characteristics Table 3 displays means and SD for the items of the FSozU K-6. In addition, item difficulties ( pi) are shown. In the total sample, the difficulty values varied between pi 5 68 (I receive a lot of understanding and security from others.) and pi 5 79. (There is someone very close to me whose help I can always count on.) The mean sum score

Table 2. Demographic characteristics of the study sample Sample characteristics Age Mean (SD) Median Range Age group, N (%) !25 yr 25e34 yr 35e44 yr 45e54 yr 55e64 yr 65e74 yr 75 yr Living with a partner, N (%) Years of education, N (%) 8 yr 9e11 yr 12 yr Current student Missing Employment status Pupil/student Working (!35 h) Unemployed Homemaker Retired Household income in V !1,250 1,250e2,500 2,500 Missing Abbreviation: SD, standard deviation.

Total sample (N [ 2,508)

Men (N [ 1,174)

Women (N [ 1,334)

49.67 (18.30) 50.00 14e92

49.16 (18.18) 50.00 14e92

50.12 (18.44) 50.00 14e92

257 360 382 445 454 381 229 1,315

(10.2) (14.4) (15.2) (17.7) (18.1) (15.2) (9.1) (52.4)

134 152 180 213 225 177 93 663

(11.4) (12.9) (15.3) (18.1) (19.2) (15.1) (7.9) (56.5)

123 208 202 232 229 204 136 652

(9.2) (15.6) (15.1) (17.4) (17.2) (15.3) (10.2) (48.9)

942 1,023 455 78 10

(37.6) (40.8) (18.1) (3.1) (0.4)

432 453 238 45 6

(36.8) (38.6) (20.3) (3.8) (0.5)

510 570 217 33 4

(38.2) (42.7) (16.3) (2.5) (0.3)

192 1,259 189 104 745

(7.7) (50.2) (7.6) (4.1) (29.7)

103 651 85 4 329

(8.8) (52.8) (7.2) (0.3) (28.0)

89 608 104 100 416

(6.7) (45.6) (7.8) (7.5) (31.2)

517 1,156 769 76

(20.6) (45.7) (97.0) (3.0)

197 527 417 33

(17.3) (44.9) (35.5) (2.8)

320 619 352 43

(24.0) (46.4) (26.4) (3.2)

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Table 3. Mean (M), SD, item difficulty (Pi), corrected itemetotal correlation (rit), and group differences for the F-SozU K-6 items and total scores Item English

Total German

I receive a lot of Ich erfahre von anderen viel understanding and Verst€andnis und security from others. Geborgenheit. There is someone very close Ich habe einen sehr to me whose help I can vertrauten Menschen, always count on. mit dessen Hilfe ich immer rechnen kann. If I need to, I can borrow Bei Bedarf kann ich mir something from friends ohne Probleme bei Freunden oder Nachbarn or neighbors without any problems. etwas ausleihen. I know several people with Ich kenne mehrere whom I like to do things. Menschen, mit denen ich gerne etwas unternehme. When I am sick, I can ask Wenn ich krank bin, kann friends/relatives to ich ohne Z€ogern Freunde/ handle important things Angeh€orige bitten, €r mich for me without hesitation. wichtige Dinge fu zu erledigen. If I’m very depressed, I Wenn ich mal sehr €ckt bin, weiß ich, know who I can turn to. bedru zu wem ich damit ohne weiteres gehen kann. F-SozU K-6 mean score

M

SD

Men Pi

rit

M

SD

Group difference

Women Pi

rit

M

SD

Pi

rit

t

3.73 0.93 68 0.70 3.69 0.94 67 0.68 3.78 0.91 70 0.67

2.40*

4.17 0.94 79 0.76 4.15 0.94 79 0.75 4.18 0.94 80 0.74

0.75

3.98 0.94 75 0.69 3.95 0.95 74 0.65 4.00 0.93 75 0.68

1.33

4.02 0.95 76 0.68 4.04 0.95 76

.64 4.01 0.94 75 0.69

0.69

4.10 0.93 78 0.80 4.09 0.92 77 0.77 4.10 0.93 78 0.79

0.35

4.06 0.97 77 0.79 4.02 1.00 76 0.79 4.10 0.94 78 0.75

1.87

4.01 0.76 d

1.36

d

3.99 0.77 d

d

4.03 0.75 d

d

Abbreviation: SD, standard deviation. *P ! 0.05. WHO-conform forwardebackward translation from German to English independently carried out by (in each case) two native speakers of the target language. Discrepancies were discussed in an expert panel with the result of a consensual solution.

of the F-SozU K-6 was 4.01 (SD 5 0.76), with a range from 1 to 5 points. At the item level, there were no statistically significant differences in the item values between men and women. In addition, the corrected itemetotal correlation values (rit) are listed in Table 3. The value characteristics in the total sample, which were between rit 5 0.68 (I know several people with whom I like to do things.) and

rit 5 0.80 (When I am sick, I can ask friends/relatives to handle important things for me without hesitation.), can be regarded as very satisfactory. Fig. 2 illustrates the dependence of the F-SozU K-6 sum score from age and sex. A two-factorial analysis of variance with the factors sex and age (eight levels: corresponding to the norm allocation) showed a significant main effect of age, F (6,

Fig. 2. The F-SozU K-6 values depending on age and gender (A) Women, (B) Men.

S. Kliem et al. / Journal of Clinical Epidemiology 68 (2015) 551e562

559

Table 4. Normative data from the general population (N 5 2,508) for the F-SozU-6 F-SozU mean score 1.00 1.17 1.33 1.50 1.67 1.83 2.00 2.17 2.33 2.50 2.67 2.83 3.00 3.17 3.33 3.50 3.67 3.83 4.00 4.17 4.33 4.50 4.67 4.83 5.00

Total 14e91 yr (N [ 2,508)

14e24 yr (N [ 257)

25e34 yr (N [ 360)

35e44 yr (N [ 382)

45e54 yr (N [ 445)

55e64 yr (N [ 454)

65e74 yr (N [ 381)

‡75 yr (N [ 229)

0 0 0 1 1 1 2 3 3 5 7 10 14 17 21 25 31 38 49 57 66 73 82 89 !99

0 0 0 0 0 0 0 1 1 1 2 4 7 9 12 14 18 23 36 44 55 66 77 87 !99

0 1 1 1 2 2 3 3 5 6 7 10 13 18 22 25 29 38 48 55 61 67 76 85 !99

0 0 0 1 1 1 2 3 4 5 7 9 11 14 18 22 26 34 44 53 60 68 79 86 !99

0 0 0 0 1 1 2 3 4 6 9 10 15 20 25 28 37 42 54 63 70 77 85 92 !99

0 0 0 0 0 1 1 2 3 3 7 9 14 17 22 27 32 39 52 60 68 76 84 90 !99

1 1 1 1 1 1 1 2 3 4 6 9 13 15 18 24 30 40 49 59 70 77 84 91 !99

0 0 0 0 0 1 1 3 5 8 11 16 22 27 31 36 43 50 61 65 74 81 87 92 !99

Normative data are presented as F-SozU-6 mean scores with corresponding percentiles. Percentiles are shown for the total sample and for subsamples based on age and gender.

2,480) 5 8.14, P ! 0.001, a nonsignificant main effect of gender, F (1, 2,480) 5 1.68, P 5 0.195, and a nonsignificant age  gender interaction effect, F (6,2,480) 5 1.37, P 5 0.221. Thus, in addition to general norms, agespecific norms will be provided (Table 4). Because the empirical distribution of the F-SozU K-6 sum scores deviated from a normal distribution, the F-SozU K-6 sum scores were transformed into percentiles. 4.2.3. Internal consistency Internal consistency for the total sample was a 5 0.90 (men: a 5 0.90; women: a 5 0.90). 4.2.4. Factorial validity Based on the Gþ statistic, n 5 26 (1.0%) individuals were excluded from this analysis. CFA revealed very good fit parameters for the general factor model. All assessed indices showed an adequate to very good model fit for the total sample [SRMR 5 0.024; RMSEA 5 0.068, 90% confidence interval (0.060, 0.077), CFI 5 0.978, TLI 5 0.964]. Factor loadings were high (0.70e0.84). Thus, it can be assumed that all items are meaningful indicators of the latent construct. 4.2.5. Factorial invariance The results of the measurement invariance analysis regarding age, gender, and age  gender are depicted in Supplementary Material (e-Table 1) at www.jclinepi.com.

Regarding the CFI differences, strong invariances can be assumed for gender, age, and age  gender interaction. Regarding strict invariance, the relevant CFI difference for age  gender interaction was slightly above the cutoff value of DCFI O 0.01 as recommended by Chen [66]. For practical reasons, strict invariance can therefore be assumed. 4.2.6. Construct validity To determine evidence for validity of the F-SozU K-6, correlation coefficients were calculated with related instruments. As can be seen in Table 5, there were low but substantial correlations between the F-SozU K-6 and other self-rating inventories in the expected direction: Higher perceived social support was associated with

Table 5. Correlation coefficients between the F-SozU-6 and other selfrating questionnaires Self-rating questionnaires

F-SozU-K6

PHQ-2

GAD-2

GBB-8

F-SozU-K6 PHQ-2 GAD-2 GBB-8

1 0.26*** 0.21*** 0.26***

d

d d

d d d 1

1 0.76*** 0.56***

1 0.56***

Abbreviations: PHQ-2, Patient Health Questionnaire 2; GAD-2, Generalized Anxiety Disorder Assessment-2; GBB-8, Giessen Subjective Complaints List-8. Spearman’s correlation coefficient was used. ***P ! 0.01.

560

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lower depression (PHQ-2), lower generalized anxiety (GAD-2), and lower somatic symptom strain (GBB-8). 5. Discussion In the present study, the six-item short form of the German Social Support Questionnaire (F-SozU) was developed based on a representative German population sample. The newly developed questionnaire (F-SozU K-6) was subsequently evaluated and standardized in another independent population sample that was also representative of the general German population. The reliability of the short form was found to be comparable to the longer versions of the German Social Support Questionnaire (F-SozU K-14, F-SozU K-22) [37]. The selectivity of the F-SozU K-6 was excellent and as expected for a shortened instrument, slightly surpasses the range of the F-SozU K-14 [42]. The mean value of the F-SozU K-6 is similar to the F-SozU K-14 [37] with a somewhat higher standard deviation, closer to the standard deviation of a standard normal distribution, thus indicating a higher degree of differentiation. As the kurtosis of the F-SozU K-6 sum scores is lower than the kurtosis of the F-SozU K-14, it seems unlikely that the higher standard deviation is a result of a high number of extreme values. In accordance with associations found with the F-SozU and its related short forms (F-SozU K-14 and F-SozU K-22), we found comparable negative correlations with depression, anxiety, and somatic symptom strain [37]. The one dimensionality of the F-SozU K-6 was confirmed on the basis of CFA. Hence, a unidimensional interpretation of the total score is given comparable to the F-SozU K-14 [42]. Furthermore, the analyses showed comparable factor structures in the subsamples that were studied (with regard to age, gender, and age  gender). The existence of strict invariance and the associated possibility of unbiased comparison of means and correlation coefficients, as well as path coefficients within structural equation models between the aforementioned groups, appear to be particularly relevant. 5.1. Limitations Despite the number of strengths of this study, for example, the large sample size and its representativeness, certain limitations should be mentioned. First, the response rate was only 57.5%. However, compared with clinical studies, a lower response rate is quite common in general population studies. Furthermore, the response rate was comparable to other general population surveys [5,68,69]. Over and above, a selection bias seems unlikely because the study sample corresponds to data from the general population with regard to demographic characteristics. Second, because the study sample is representative of the general population of Germany, comparisons only with Western European and white American populations seem appropriate. In future research, investigators should try to

replicate our findings in different (eg, Chinese or South African) and also more heterogeneous cultures. 5.2. Conclusion In summary, in spite of some limitations, the F-SozU K-6 provides an economical and reliable instrument for evaluating the degree of perceived social support. It is conceivable that it could be used within the framework of clinical epidemiologic studies. Based on a German representative population sample, norm values and pragmatic cutoff points can be provided as a practical classification of available social support. The inventory also provides for an undistorted comparison of measurement values from both sexes across the full lifespan (14e92 years). Acknowledgments Authors’ contributions: S.K., M.Z., and E.B. had full access to all the data in the study and take responsibility for the integrity of the data and the accuracy of the data analysis.

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A brief form of the Perceived Social Support Questionnaire (F-SozU) was developed, validated, and standardized.

Development of a brief instrument (F-SozU K-6) for the measurement of perceived social support in epidemiologic contexts by shortening a well-establis...
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