http://informahealthcare.com/dre ISSN 0963-8288 print/ISSN 1464-5165 online Disabil Rehabil, Early Online: 1–10 ! 2015 Informa UK Ltd. DOI: 10.3109/09638288.2015.1021022

RESEARCH PAPER

Further validation of the Multiple Sclerosis Self-Efficacy Scale Chung-Yi Chiu and Robert W. Motl

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Department of Kinesiology and Community Health, University of Illinois at Urbana-Champaign, Champaign, IL, USA

Abstract

Keywords

Purpose: This study examined the factorial and construct validity of the Multiple Sclerosis SelfEfficacy (MSSE) Scale in two samples of people with multiple sclerosis (MS). Method: Two samples (n’s ¼ 292, 275) of participants with MS were recruited from across the United States. Participants in both studies completed a questionnaire battery that included the MSSE and measures of symptoms, dysfunction, disability, psychosocial aspects, mental/emotional wellbeing, and quality of life. Factorial validity was tested using confirmatory factor analysis (CFA), whereas construct validity was examined based on bivariate correlations with scores from other measures. Results: The two-factor measurement model provided a poor fit for the 18 items on the MSSE in both the samples. This model provided a good fit for a modified, 10-item scale in both samples. The 10-item version of the MSSE was highly correlated with the original MSSE (r ¼ 0.97, p50.001) and related constructs (e.g. disability, r ¼ 0.69, p50.0001). The standardized Cronbach’s as of the two subscales (function and control) of the 10-item version ranged between 0.78 and 0.94 for both samples. Conclusions: Scores from the modified, 10-item version of the MSSE provide a valid and reliable measure of MS-specific self-efficacy among persons with MS.

Factor analysis, measurement, multiple sclerosis, psychometrics, self-efficacy History Received 12 October 2014 Revised 10 February 2015 Accepted 16 February 2015 Published online 9 March 2015

ä Implications for Rehabilitation  





The importance of self-efficacy in managing the consequences of multiple sclerosis (MS) has increased. The Multiple Sclerosis Self-Efficacy (MSSE) Scale was developed and validated for measuring self-efficacy in function maintenance and control over MS from patients’ perspectives. In the past almost 20 years, this scale has not undergone additional validation of its factor structure and construct validity in large-scale samples of persons with MS. The original two-factor construct did not provide a good fit for the 18 items on the MSSE in two independent samples. We modified the MSSE and found the 10 items fitted by the twofactor construct well with one sample and demonstrated cross-validity of the 10 items in the second sample. The 10-item version of the MSSE has good reliability and construct validity in both independent samples. Researchers and clinicians should adopt these 10 items when examining MS self-efficacy of patients.

Introduction Multiple sclerosis (MS) is a chronic, unpredictable, and debilitating disease of the central nervous system [1–3]. This disease results in many, heterogeneous symptoms, functional declines, reduced quality of life, and disability associated with engaging in daily activities (e.g. self-care, work/learning, and/or recreation) and roles (e.g. worker, partner, friend, and/or parent). This creates a particularly burdensome disease that requires a high degree of

Address for correspondence: Chung-Yi Chiu, PhD, CRC, Department of Kinesiology and Community Health, University of Illinois at UrbanaChampaign, 1206 South Fourth Street, Champaign, IL 61820, USA. Tel: 1-217-244-6435. Fax: 1-217-333-2766. E-mail: [email protected]

coping resources for successfully managing the consequences and lifelong burdens of MS. Self-efficacy might represent an important source of coping for managing the consequences, burdens, and stress of MS [4–6]. Self-efficacy can be described as the belief in one’s ability to successfully undertake or execute a course of action for achieving desired outcomes [7]. Self-efficacy expectations influence the course of actions, thought processes, and resources that a person will undertake and adopt for managing and achieving desired outcomes [7]. For example, self-efficacy can represent a lens for interpreting one’s reactions and experiences in daily life when living with a chronic disease. Self-efficacy further influences health behaviors that will be adopted for managing disease outcomes and consequences [4,6]. We finally note that selfefficacy expectations can be manipulated based on targeted

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C.-Y. Chiu & R. W. Motl

sources of efficacy information in the context of research and clinical practice for possibly managing the consequences of MS [8,9]. Such theoretical, research, and clinical relevance supports the importance of studying self-efficacy in the context of MS. The study of self-efficacy in MS requires measures with evidence supporting the validity and reliability of scores. To that end, Schwartz et al. developed the Multiple Sclerosis SelfEfficacy (MSSE) Scale for measuring self-efficacy specifically among persons with MS [10]. The MSSE was initially developed by including 14 of the original 20 items from the Arthritis SelfEfficacy Scale (ASES) [11]; the 14 items from the ASES were modified, as necessary, for the context of MS. The MSSE included 10 additional items that reflected MS-symptoms (e.g. cognition and fatigue). The 24 items on the MSSE were rated on a scale from 10 to 100, where 10 has an anchor of very uncertain, 50 moderately certain, and 100 very certain. The researchers administered the original 24-item scale among 141 persons with neurologist confirmed relapsing-remitting or chronic progressive MS for principle components analysis (PCA) and item reduction, internal consistency, and construct validation [10]. The PCA identified 18 items that were represented by two subscales of Function (9 items) and Control (9 items). Items on the Function subscale reflected confidence in performing behaviors associated with engaging in daily living activities, where the Control subscale items reflected confidence in managing disease symptoms, reactions, and impact on daily life activities. The standardized a for all 18 items was 0.89, and it was 0.86 and 0.90 for the subscales of Function and Control, respectively [10]. Regarding construct validity, the Function subscale was highly correlated negatively with the physical role limitation subscale of the Sickness Impact Profile (r ¼ 0.73, p50.001) and the Expanded Disability Status Scale (r ¼ 0.64, p50.001) [10]. The Control subscale was highly correlated positively with the environmental mastery subscale of Ryff Happiness scale (r ¼ 0.50, p50.001) [10]. Such evidence supports the promise of the MSSE for inclusion in research and clinical practice of persons with MS, but validity is an ongoing and evolving process wherein researchers replicate previous results and extend the analyses for strengthening the psychometric properties of a scale [12]. The present study further examined the validity and reliability of the MSSE in two, separate and large samples of persons with MS. We first applied confirmatory factor analysis (CFA) for replicating and cross-validating the latent structure of the 18-item MSSE among people with MS recruited by convenience sampling from a general community context. We then examined the reliability (internal consistency, standardized Cronbach’s a) of the MSSE and its subscales, and comprehensively examined the construct validity of the MSSE based on its association with scores from other measures common in studies of MS. This included measures of relevance for self-efficacy for establishing convergent aspects of construct validity (e.g. MS symptoms, pain, fatigue, depression, and quality of life). Such additional analyses with this scale seem particularly salient, given the regular adoption of the MSSE in research on MS [13–16].

Methods This study involved a secondary analysis of existing data from two independent samples. Sample 1 was from a previously completed examination study of change in quality of life over time and its predictors for people with MS [17]. Sample 2 was from a study examining longitudinal change in physical activity and its correlates in relapsing-remitting MS (RRMS) [18]. Detailed recruitment information and protocols of these two studies have been described. We provided a brief overview of samples and study protocols below.

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Participants Sample 1 (n ¼ 292): calibration sample This sample completed a set of surveys related to MS selfefficacy and the 18-item MSSE. We used this sample for calibrating the two-factor construct of the 18-item MSSE and examining construct validity by the set of surveys. The convenience sample of people with MS was recruited from three chapters of the National MS Society, the Greater Illinois, Gateway, and Indiana chapters for the study of intermediate variables in the association between changes in physical activity and quality of life [17]. The participants were asked to contact the research team through either e-mail or a toll-free telephone, and collect calls were encouraged and accepted from those interested in participating and living outside the local calling area. This initial contact was followed-up by a phone call from a member of the research team who described the study and its procedures, answered all questions and conducted a brief screening interview. The screening criteria involved (a) having an established definite diagnosis of MS, (b) being relapse free in the last 30 days, and (c) being ambulatory with minimal assistance. The definite diagnosis was confirmed based on completion of a form-letter by the participant’s neurologist. Individuals were relapse free as we suspect that physical activity would be substantially reduced during and immediately after such an episode. Ambulatory with minimal assistance was defined as being able to walk with or without a cane, but excludes those using a wheelchair or motorized cart. Initially, 511 persons with MS contacted the research team and 387 of those underwent screening. Of those 387 participants, 27 turned out not qualified, and 16 declined participation. We sent an informed consent document and verification letter to the remaining 344 individuals, and the forms were returned by 300 of the 344 individuals. Of those who returned the forms, eight did not continue with participation and reasons for lack of participation are unknown. The final convenience sample consisted of 292 individuals with MS. There were 237 persons with RRMS, 12 with primary progressive MS, 34 with secondary progressive MS, and 7 with benign MS. The mean age of the sample was 48.0 years (SD ¼ 10.3, range ¼ 20–84 years) and the mean duration, defined as time since definite diagnosis, of MS was 10.3 years (SD ¼ 7.9, range ¼ 0.5–37.0 years). The sample was mostly Caucasian (93%), married (68%), employed (52%), and educated (28% had some college education and 57.6% were college graduates) with a median annual household income of greater than $40 000 (65.4%). In average, they evaluated their perceived disability is at 2.34 upon the 0–8 Likert-type scale of the Patient Determined Disease Step [19] where 0 means normal, 1 means mild disability, 2 means moderate disability, 3 means gait disability, 4 means early cane, 5 means late cane, 6 means bilateral support, 7 means wheelchair, and 8 means bedridden. Sample 2 (n ¼ 275): cross-validation sample We used this sample for subsequently cross validating the construct of the 18-item or shorter form of the MSSE. The convenience sample of people with MS was recruited from the National MS Society website of the headquarters and 12 chapters of the National MS Society in Midwestern for the study of a longitudinal investigation of symptoms and physical activity over 2.5 years on persons with RRMS [18]. The interested participants were asked to contact the research team through either e-mail or a toll-free telephone call. This initial contact was followed-up by a phone call from a member of the research team who described the study and its procedures, answered all questions, and conducted a brief screening interview. The screening criteria involved:

Self-efficacy in MS

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DOI: 10.3109/09638288.2015.1021022

(a) diagnosis of RRMS confirmed by a physician, (b) relapse-free in the previous 30 days, (c) ambulatory with or without assistance (i.e. walk independently or walk with a cane or crutch or walker or rollator), and (d) willingness to complete the study materials every 6 months over 2.5 years. Those who did not satisfy the inclusion criteria were excluded from participation. We successfully contacted 375 of the 463 people who expressed interest in the study, and 6 were uninterested in participation after the description of the study procedures. The remaining 369 people underwent screening, 44 did not satisfy the inclusion criteria, and 5 declined voluntary participation. We sent an informed consent document (completed by the participant) and RRMS verification form (completed by the participant’s treating physician) to the remaining 320 people, and 41 did not return the documents despite 3 attempts for follow-up contact. We sent study materials to the remaining 279 people. We finally received 275 returned packets. The mean age of the sample was 45.9 years (SD ¼ 9.7, range ¼ 19–64 years) and the mean duration, defined as time since definite diagnosis of RRMS was 8.87 years (SD ¼ 7.1, range ¼ 0.1–36.0 years). The sample was mostly Caucasian (91%), married (70%), employed (58%), and educated (25% had some college education and 57.3% were college graduates) with a median annual household income of greater than $40 000 (67%). In average, they evaluated their perceived disability is at 1.96 upon the 0–8 Likert-type scale of the Patient Determined Disease Step [19]. Instruments

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older adults [24]. The abbreviated LLFDI has two subscales, function and disability. The subscale of function has 15 items asking about how much difficultly to perform physical activities involved in upper extremity, basic lower extremity, and advanced lower extremity, rated on a 5-point Likert-type scale from 1 (cannot do) to 5 (none) (Internal consistencies ¼ 0.58, 0.76, and 0.85, respectively) [24]. The subscale of disability has 8 items, rated on a 5-point Likert-type scale of two perspectives, limitation of capability rated on a 5-point Likert-type scale from 1 (completely limited) to 5 (not at all) and frequency of performance rated on a 5-point Likert-type scale from 1 (never) to 5 (very often) [24]. Each perceptive was divided into a social and personal role. The internal consistency of the social and personal role of the disability-function subscale were 0.67 and 0.38, respectively [24]. The internal consistency of the social and personal role of the disability-limitation subscale were 0.83 and 0.77, respectively [24]. The abbreviated LLFDI was correlated significantly with the original LLFDI at r ¼ 0.78–0.90 [25,26]. The present study used the subscale scores of function and disability. The PDDS is a self-report questionnaire that contains a single item for measuring self-reported disability using an nine-level ordinal scale [19], rated from 0 indicating ‘‘normal-I may gave some mild symptoms, mostly sensory due to MS but they do not limit my activity’’ to 8 meaning ‘‘bedridden-unable to sit in a wheelchair for more than one hour’’. Scores from the PDDS are linearly and strongly related with physician-administered EDSS scores (r ¼ 0.93, p50.05) [19].

MS Self-Efficacy Scale We described the MSSE in the ‘‘Introduction’’ section. Symptom, dysfunction and disability Symptom, dysfunction and disability were measured by the Symptom Inventory (SI) [20,21], the short-form McGill Pain Questionnaire (SF-MPQ) [22], Fatigue Severity Scale (FSS) [23], abbreviated Late-Life Function and Disability Instrument (LLFDI) [24], and the Patient Determined Disease Steps (PDDS) [19]. The SI has 99 items measuring the severity of MS neurological impairment experienced during the past month, rated on a 5-point Likert-type scale from 0 (not at all) to 4 (a great deal) [20,21]. The SI was composed of six subscales such as visual (8 items), left hemisphere (23 items), right hemisphere (8 items), brainstem and cerebellum (16 items), spinal cord (36 items), and nonlocalized symptoms (8 items). The test–retest reliability of the SI was 0.92 (p50.05) [20,21]. Its standardized a was 0.97 in the present study. Pain was measured with the SF-MPQ [22]. This scale has a 15-item adjective checklist that captures sensory and affective dimensions of pain experienced during the past 4 weeks. The items were rated on a 4-point Likert-type scale that ranged between 0 (none) and 3 (severe). The items were summed to form a composite that ranged between 0 and 45 [22]. Higher scores reflect more severe pain. The SF-MPQ is internally consistent, reliable across time, and has evidence of score validity [22]. Coeffcient a for the SF-MPQ was 0.88 in the present study. The FSS has 9 items that are combined to form an overall measure of a person’s severity of fatigue symptoms [23]. The items were rated on a 7-point Likert-type scale that ranged between 1 (strongly disagree) and 7 (strongly agree). The items were summed to form a composite that ranged between 9 and 63 [23]. This scale has good evidence of internal consistency, test– retest reliability, and score validity [23]. Coefficient a for the FSS was 0.93 in the present study. The abbreviated LLFDI is a self-report questionnaire that evaluates physical function and disability in community-dwelling

Psychosocial aspects We used the Exercise Self-efficacy Scale (EXSE) [27] and Social Provisions Scale (SPS) [28]. The EXSE has 6 items asking how much confidence one has to participate in physical activity three times per week at moderate intensity for 20 and/or more minutes in the future (e.g. next month, next 2 months, etc.) [27]. The internal consistency was at 0.90. The EXSE was significantly correlated with the barriers self-efficacy of exercise scale (r ¼ 0.88, p50.05) [27]. The internal consistency of the EXSE in the present study was 0.99. The SPS measures social support and provisions in a person’s networks by six subscales of reliable alliance, attachment, guidance, nurturance, social integration and reassurance of worth, rated on a 4-point Likert-type scale from 1 (strongly disagree) to 4 (strongly agree) [28]. Cutrona and Russell recruited 1792 participants, including 1183 college students, 303 public school teachers, and 306 nurses [28]. Overall, the Cronbach’s a of attachment was 0.75, social integration was 0.67, reassurance of worth was 0.67, reliable alliance was 0.65; guidance was 0.76, and opportunity for nurturance was 0.66 [28]. The overall scale had an a of 0.92 [28]. The test–retest of the SPS ranging between 0.37 and 0.66 [28]. The internal consistency of the SPS in the present study was 0.89. Mental/emotional well-being We used the Hospital Anxiety and Depression Scale (HADS) [29] and the Satisfaction With Life Scale (SWLS) [30]. The HADS measures moods of anxiety and depression during the past week [29]. The HADS contains 14 items; 7 items measure anxiety and 7 items measure depression, rated on a 4-point Likert-type scale from 0 (not at all) to 3 (most of the time) [29]. The internal consistency of the anxiety subscale was 0.80, 0.81 for the depression subscale. This scale has been used in previous studies of quality of life in MS [31] and has good evidence of score reliability and validity [29]. Coefficient a for the anxiety and depression components of the HADS were 0.83 and 0.82, respectively, in the present study.

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C.-Y. Chiu & R. W. Motl

The SWLS was designed to measure one’s global assessment of global judgments of subjective well-being in different life domains based on his/her values and standards [30]. The SWLS has 5 items rated on a 7-point Likert-type scale from 1 (strongly disagree) to 7 (strongly agree). The SWLS has good internal consistency, test–retest reliability, and evidence of score validity [30,32]. The internal consistency ranged from 0.80 to 0.96 in several studies [30,33]. The factor analysis study was found only one single dimension of the SWLS [30,34]. Coefficient a for the SWLS was 0.89 in the present study.

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Quality of life Quality of life was measured by the Short Form-12 (SF-12) [35], Multiple Sclerosis Impact Score (MSIS-29) [36], and Leeds Multiple Sclerosis Quality of Life Scale (LMSQOL) [37]. The SF-12 was to operationalize the concept of healthy-related quality of life. It is composed of 12 items and eight subscales [35]. Items are rated on either a 5-point Likert-type scale (1 ¼ excellent to 5 ¼ poor) for Items 1 and 4 through 12 or a 3-point Likert-type scale (1 ¼ yes, limited a lot to 3 ¼ no, not limited at all) for Items 2 and 3. The 12 items are summed as a Physical Component Summary Scale (PCS) and a Mental Component Summary Scale (MCS). The scores are standardized in the general population (M ¼ 50, SD ¼ 10) [35]. Test–retest reliability estimated over a 2-week interval was 0.89 of the SF-12 PCS and 0.76 of the SF-12 MCS [35]. The MSIS-29 has 29 items, 20 items for measuring physical disability and 9 items for evaluating psychological impact of MS [36]. The internal consistency for the physical subscale was 0.86, 0.80 for the psychological subscale [38]. The physical subscale was significantly correlated highly with the physical component of SF-12 (r ¼ 0.77), but with mental component of SF-12 at 0.50 [36]. The psychological subscale was significantly correlated highly with mental component of SF-12 (r ¼ 0.77), but with physical component of SF-12 at 0.57 [36]. The LMSQOL was a MS-specific measure of quality of life [37]. It has 8 items generated from the interviews with people with MS regarding their main concerns in living with MS [37]. The LMSQOL was significantly correlated with the General Well Being Index at 0.83. Its internal consistency was 0.79 and testretest reliability was 0.85, with no floor or ceiling effects. The internal consistency in the present study was 0.82 [37]. Data analysis The data were analyzed with Mplus 7.0 [39] and the Statistical Package for the Social Sciences (SPSS, version 22.0, Armonk, NY) [40]. The two-factor structure of the MSSE was analyzed using CFA with the Maximum Likelihood Robust (MLR) estimator in Mplus. The MLR estimator provides maximum likelihood parameter estimates with standard errors and a chisquare test statistic that are robust to non-normality and nonindependence of observation [39]. Model-data fit was assessed using the chi-square goodness-of-fit test, the comparative fit index (CFI), the root mean square error of approximation (RMSEA), and the standardized root mean square residual (SRMR) [41]. A non-significant chi-square or values greater than 0.90 for the CFI are considered an acceptable model fit, with a value of 0.95 or higher considered an excellent fit. For RMSEA, a value of less than 0.05 indicates a close fit and values of up to 0.08 indicate reasonable errors of approximation in the population. For SRMR, a value of less than 0.08 indicates a good fit and less than 0.10 is a mediocre fit. Furthermore, the modification index (MI) above 20 of a measure item was considered whether such items are redundant. We balanced our consideration based on statistical

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analysis and item-content review for achieving precision and conciseness of an assessment with good psychometrics. Descriptive statistics were computed for all study variables. Standardized Cronbach’s coefficient a was computed to evaluate the internal consistency reliability of the MSSE and its subscales. Pearson product–moment correlations were computed to determine the construct validity by examining the relationships among MSSE total and subscale scores with the following measures that reflects each construct. For testing the construct of symptom, dysfunction and disability, we used SI, SF-MPQ, FSS, LLFDI, and PDDS. For testing the construct of psychosocial aspects, we used EXSE and SPS. For testing the construct of mental/ emotional well-being, we used HADS and SWLS. For testing the construct of quality of life, we employed SF-12, MSIS-29, and LMSQOL. Table 2 summarizes the above measures along with its reflected constructs. The correlation coefficients of 0.10, 0.30, and 0.50 are the strength of correlations between the MSSE and construct measures at the small, moderate, and large magnitudes, respectively. We hypothesized that (1) the two-factor construct of the 18-item MSSE would be valid across multiple independent groups; (2) the 18-item MSSE overall would be correlated with perceived symptoms, dysfunction and disability; psychosocial aspects; mental/emotional well-being; and general and MSspecific quality of life; (3) the Function subscale of the 18-item MSSE which evaluates activities of daily living would have stronger correlations with physical health and impairments and the physical dimension of quality of life than with mental/social well-being and emotional disorders and psychological dimension of quality of life; (4) the Control subscale of the 18-item MSSE which evaluates symptom management and mental/emotional regulation of impacts from MS would have stronger correlations with mental/social well-being, emotional disorders, and psychological dimension of quality of life than with physical health and impairments and the physical dimension of quality of life.

Results In sum of sample comparison, the age of Sample 1 was about 2 years older than the Sample 2 (t (df ¼ 564) ¼ 2.49, p ¼ 0.013). The Sample 1 had lived with MS 1.40 years more than the Sample 2 (t (df ¼ 564) ¼ 2.23, p ¼ 0.026). The Sample 1 had different types of MS courses while the Sample 2 focused mainly on RRMS. Notably, the Sample 1 has apparently reported disabled severer than the Sample 2 (t (df ¼ 564) ¼ 2.62, p ¼ 0.009). In terms of selfreported MS specific self-efficacy, there were no significant differences between two independent samples (Table 1). Table 2 lists the means, standard deviations and ranges of all measures used in the present study. Factorial validity and internal consistency of the MSSE The two factor model of the MSSE did not fit the data of Sample 1 and Sample 2 (Table 3). We then considered modifying the MSSE using the data of Sample 1 (i.e. calibration). There were multiple large MIs (exceeding 20) between items, for example item 14–15 (MI ¼ 83.96), item 4–8 (MI ¼ 42.76), item 10–16 (MI ¼ 35.30), item 6–7 (MI ¼ 27.81), item 10–11 (MI ¼ 23.92), item 4–5 (MI ¼ 21.89), item 10–14 (MI ¼ 21.51), and item 1–2 (MI ¼ 21.21). This indicated residual covariance unaccounted for by the two-factor measurement model, and that the content meaning of these items may be redundant. We further scrutinized these item pairs closely. Of note, all factor loadings of items on two factors were all above 0.40 in Sample 1, but a few items were relatively low (Table 4). Schwartz et al. further reported that some items had cross-factor loadings such as item 3, 6, 7, 9, 10, and 16 [10]. After considering these items from different angles in

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DOI: 10.3109/09638288.2015.1021022

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Table 1. Descriptive statistics and differences in both samples. Sample 1 (n ¼ 292)

Female ¼ 245 (83.9%) Female ¼ 229 (83.3%) Male ¼ 47 (16.1%) Male ¼ 46 (16.7%) Mean ¼ 45.94 Age Mean ¼ 48.03 SD ¼ 9.66 SD ¼ 10.29 Range ¼ 19–64 Range ¼ 20–84 Marital status Married ¼ 198 (68.0%) Married ¼ 192 (69.8%) Single ¼ 45 (15.5%) Single ¼ 41 (14.9%) Divorced/single ¼ 39 (13.4%) Divorced/single ¼ 39 (14.2%) Widow/widower ¼ 9 (3.1%) Widow/widower ¼ 3 (1.1%) Occupation status Unemployed ¼ 135 (46.2%) Unemployed ¼ 114 (41.3%) Employed ¼ 152 (52.1%) Employed ¼ 161 (58.3%) Mean ¼ 19.62 Working hours/week Mean ¼ 20.17 SD ¼ 19.90 SD ¼ 19.92 Range ¼ 0–75 Range ¼ 0–84 Race Asian ¼ 2 (0.7%) Asian ¼ 2 (0.7%) African American ¼ 9 (3.1%) African American ¼ 12 (4.3%) Caucasian ¼ 272 (93.2%) Caucasian ¼ 252 (91.3%) Latino ¼ 3 (1.0%) Latino ¼ 5 (1.8%) American Indian ¼ 0 (0%) American Indian ¼ 1 (0.4%) Other ¼ 4 (1.4%) Other ¼ 3 (1.1%) Education Less than 7th grade ¼ 0 (0%) Less than 7th grade ¼ 0 (0%) 9th grade ¼ 0 (0%) 9th grade ¼ 2 (0.7%) Partial high school ¼ 0 (0%) Partial high school ¼ 2 (0.7%) High school graduate ¼ 41 (14.0%) High school graduate ¼ 44 (15.9%) 1–3 years of college ¼ 82 (28.1%) 1–3 years of college ¼ 69 (25.0%) College/university graduate ¼ 96 (32.9%) College/university graduate ¼ 91 (33.0%) Master’s degree ¼ 61 (20.9%) Master’s degree ¼ 54 (19.6%) PhD or equivalent ¼ 11 (3.8%) PhD or equivalent ¼ 13 (4.7%) Income 5than $5,000 ¼ 6 (2.1%) 5than $5000 ¼ 4 (1.4%) $5001–10 000 ¼ 5 (1.7%) $5001–10 000 ¼ 8 (2.9%) $10 001–15 000 ¼ 13 (4.5%) $10 001–15 000 ¼ 17 (6.2%) $15 001–20 000 ¼ 13 (4.5%) $15 001–20 000 ¼ 9 (3.3%) $20 001–25 000 ¼ 12 (4.1%) $20 001–25 000 ¼ 8 (2.9%) $25 001–30 000 ¼ 16 (5.5%) $25 001–30 000 ¼ 10 (3.6%) $30 001–40 000 ¼ 26 (8.9%) $30 001–40 000 ¼ 28 (10.1%) $40 001 or greater ¼ 191 (65.4%) $40 001 or greater ¼ 185 (67.0%) MS types Relapsing-remitting MS ¼ 237 (81.2%) Relapsing-remitting MS ¼ 275 Secondary progressive MS ¼ 34 (11.6%) Primary progressive MS ¼ 12 (4.1%) Benign MS ¼ 7 (2.4%) Mean ¼ 8.87 Years since being diagnosed Mean ¼ 10.27 SD ¼ 7.07 with MS SD ¼ 7.85 Range ¼ 0.1–36.0 Range ¼ 0.5–37.0 Mean ¼ 1.96 Patient Determined Disease Step Mean ¼ 2.34 SD ¼ 1.65 SD ¼ 1.75 Range ¼ 0–6 Range ¼ 0–6 Mean ¼ 149.44 MSSE-Long form-total 18 items Mean ¼ 146.87 SD ¼ 26.77 SD ¼ 26.94 Range ¼ 39–180 Range ¼ 51–180 Mean ¼ 80.81 MSSE-Function 9 items Mean ¼ 80.79 SD ¼ 11.18 SD ¼ 10.24 Range ¼ 15–90 Range ¼ 31–90 Mean ¼ 68.63 MSSE-Control 9 items Mean ¼ 66.08 SD ¼ 18.20 SD ¼ 19.29 Range ¼ 6–105 Range ¼ 13–90 Mean ¼ 86.00 MSSE-Short form- total10 items Mean ¼ 84.39 SD ¼ 14.74 SD ¼ 14.86 Range ¼ 21–120 Range ¼ 31–100 Mean ¼ 37.87 MSSE-Function Short 4 items Mean ¼ 38.12 SD ¼ 4.71 SD ¼ 3.98 Range ¼ 7–40 Range ¼ 11–40 Mean ¼ 48.13 MSSE-Control Short 6 items Mean ¼ 46.27 SD ¼ 12.22 SD ¼ 12.69 Range ¼ 5–94 Range ¼ 10–60

Gender

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Sample 2 (n ¼ 275)

a

Differencea 2 ¼ 0.04 t

b (df¼564) ¼ 2.49

pb 0.839 0.013

2 ¼ 2.83

0.419

2 ¼ 1.77

0.183

t(df¼535) ¼ 0.32

0.749

2 ¼ 2.44

0.786

2 ¼ 5.50

0.481

2 ¼ 5.45

0.709

51.18b

0.000

t

b (df¼564) ¼ 2.23

0.026

t

b (df¼563) ¼ 2.62

0.009

t

(df¼563) ¼ 1.14

0.256

t

(df¼563) ¼ 0.02

0.982

t

(df¼564) ¼ 1.62

0.106

t

(df¼563) ¼ 1.30

0.195

t

(df¼563) ¼ 0.69

0.492

t

(df¼564) ¼ 1.77

0.077

Categorical variables’ differences were determined by the Chi-square difference test. Continuous variables’ differences were determined by the t test. The significance level is at a ¼ 0.05.

b

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C.-Y. Chiu & R. W. Motl

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Table 2. Descriptive statistics for the measures in sample 1.

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Measure Symptom, dysfunction, disability Symptom inventory SF-McGill Pain Questionnaire Fatigue Severity Scale LLFDI-Overall Function LLFDI-Disability Limitation LLFDI-Disability Frequency PDDS Psychosocial aspects Exercise Self-Efficacy Scale Social Provisions Scale-Total Mental/Emotional well-being HADS-Depression HADS-Anxiety SWLS Quality of life SF-12 PCS SF-12 MCS MSIS-29-Physical MSIS-29-Psychological Leeds MS Quality of Life Scale

Mean

SD

Range

7.36 10.73 4.97 55.03 32.58 30.67 2.34

4.07 7.77 1.44 11.77 6.13 4.35 1.75

0–20 0–33 1–7 28–75 15–40 17–40 0–6

7.21 73.77

3.29 10.19

0–10 42–92

6.05 5.85 21.81

4.17 3.76 7.96

0–18 0–18 5–35

41.82 41.48 43.83 20.48 19.32

9.12 9.14 16.66 8.00 4.81

22.59–62.72 19.38–60.81 20–97 9–43 10–31

SF-McGill Pain Questionnaire, the short-form McGill Pain Questionnaire; LLFDI, late-life function and disability instrument; PDDS, patient determined disease steps scale; HADS, hospital anxiety and depression scale; SWLS, satisfaction with life scale; SF-12 PCS, SF12-physical component summary scale; SF-12 MCS, SF12-mental component summary scale; MSIS-29, multiple sclerosis impact scale.

indicating that the MSSE-10 could be a good, effective and concise version of the original 18 items (Table 5). More interestingly, the 6-item Control subscale was very strongly correlated with the 18-item MSSE in both Samples 1 and 2, respectively (r ¼ 0.94, 0.93, p50.0001). Across Samples 1 and 2, the correlation coefficients of the 6-item Control subscale and the 18-item MSSE were obviously higher than the correlation coefficients of the 4-item Function subscale and the 18-item MSSE (Table 5). Construct validity Using the data of Sample 1, the 18-item MSSE and the MSSE-10 had highest coefficients with the limitation dimension of the LLFDI-Disability subscale and the physical subscale of the MSIS29, while the 18-item MSSE has the moderate strength of correlations with all other measures used in the present study (Table 6). As we hypothesized, the Function subscale of the 18-item MSSE had stronger correlations with physical health and impairments and the physical dimension of quality of life than with mental/social well-being and emotional disorders and psychological dimension of quality of life. Likewise, the Control subscale of the 18-item MSSE had stronger correlations with mental/social well-being, emotional disorders, and psychological dimension of quality of life than with physical health and impairments and the physical dimension of quality of life. Interestingly, the 6-item Control had dominantly correlated more strongly with all construct measures than the 4-item Function subscale with all these measures (Table 6).

Discussion Table 3. Model fits of sample 1 and 2, respectively. Long form

Items Factors 2/df CFI TLI RMSEA SRMR

Short form

Sample 1

Sample 2

Sample 1

Sample 2

18 2 440.663/134 0.833 0.810 0.089 0.081

18 2 522.672/134 0.793 0.764 0.103 0.092

10 2 59.405/34 0.968 0.958 0.051 0.059

10 2 75.385/34 0.949 0.932 0.067 0.042

CFI, comparative fit index; TLI, Tucker–Lewis index; RMSEA, root mean square error of approximation; SRMR, standardized root mean square residual.

terms of statistical results, item content analysis, and previous empirical evidence, we systematically removed 5 items in the Function subscale and 3 items in the Control subscale (Table 4). This modified, two-factor, 10-item version of the MSSE (MSSE-10) provided an excellent fit for the data in Sample 1 (Table 3). The MIs were relatively low (less than 20). To this point, we did not consider further modifications. This model provided an excellent fit for the data in Sample 2 (i.e. crossvalidity), and the MIs were all less than 23. This model fit was acceptable and satisfying. The MSSE-10 had as high internal consistency of each constructs across independent samples as above 0.78 (Table 4).

Self-efficacy in coping with MS has been regarded as a critical, instrumental belief in MS patients. Such a belief has profound influences on physical and mental health, psychosocial adjustments, and quality of life for people with MS. It is valuable to validate an effective, reliable and efficient measure of MS selfefficacy for clinicians to know what kind and how much selfefficacy a patient has developed. It further helps clinicians to provide appropriate self-efficacy intervention. The 18-item MSSE was the first measurement evaluating self-efficacy in MS; however, it has not undergone an additional examination since its first validation study by Schwartz et al. [10], who recruited patients under psychosocial interventions and examined its construct validity by the three constructs of physical role limitations, neurological function and environmental mastery. However, self-efficacy in MS is related to broader constructs. It was thus needed to further validate the 18-item MSSE by participants with MS not receiving psychosocial interventions and by comprehensive constructs related to aspects such as symptoms, dysfunction and disability, psychosocial aspects, psychological well-being, and quality of life. We examined the 18-item MSSE with people with MS not receiving self-efficacy interventions and determined that the two-factor constructs of the 18-item MSSE failed to fit our empirical data well. After re-specifying the 18item MSSE and validating the two-factor construct of the revised MSSE across two independent samples, we recommended 10 of the 18 items (MSSE-10). The standardized internal consistency of the MSSE-10 is high. The MSSE-10 has moderate to high correlated coefficients with multiple bio-psycho-social constructs. Factorial validity and internal consistency

Correlations between the 18-item MSSE and the 10-item MSSE (MSSE-10) The correlations between the 18-item MSSE and the MSSE-10 in each sample were all very high (both r ¼ 0.97, p50.0001),

The reasons why the 18-item MSSE failed to fit the current data could be because some of the original items have close factor loadings across both Function and Control and/or the factor loadings were lower than 0.40, such as ‘‘you can speak clearly to

Self-efficacy in MS

DOI: 10.3109/09638288.2015.1021022

7

Table 4. Factor loadings and standardized internal consistencies of the long and short forms of the MSSE in sample 1 and 2, respectively. Long form

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Itemsb 1. How confident are you that you can walk 100 feet on flat ground? 2. How confident are you that you can walk 10 steps downstairs? 3. How confident are you that you can take good care of your home or yard? 4. How confident are you that you can get dressed or undress without assistance? 5. How confident are you that you can get in and out of the passenger side of a car without assistance from another person or without physical aids? 6. How confident are you that you can speak clearly to express your needs or ideas? 7. How confident are you that you can write clearly so that others can read what you wrote? 8. How confident are you that you can take a bath or shower without assistance from someone else? 9. How confident are you that you can go on a trip that keeps you away from home for the whole day? 10. How confident are you that you can control your fatigue? 11. How confident are you that you can regulate your activity so as to be active without aggravating your MS? 12. As compared to other people with MS like yours, how confident are you that can manage your MS symptoms during your daily activities? 13. How confident are you that you can manage your symptoms so that you can do things you enjoy doing? 14. How confident are you that you can deal with the frustration of MS? 15. How confident are you that you can deal with the uncertainty of MS? 16. How confident are you that you can decrease your fatigue quite a bit? 17. How confident are you that you continue most of your daily activities? 18. How confident are you that you can keep your MS symptoms from interfering with your time spent with friends and family?

Short form

Sample 1 Factor loading Function (0.832)a

Sample 2 Factor loading Function (0.858)a

Sample 1 Factor loading Function (0.780)a

Sample 2 Factor loading Function (0.825)a

0.623

0.466

0.614

0.557

0.510

0.540

0.495

0.624

0.707

0.718

0.916

0.820

0.700

0.763

0.680

0.836

0.535

0.624

0.580

0.646

0.602

0.721

0.686

0.766

0.542

0.603

Control (0.947)a 0.748

Control (0.914)a 0.751

Control (0.936)a

Control (0.880)a

0.782

0.796

0.762

0.768

0.813

0.874

0.825

0.885

0.891

0.882

0.897

0.897

0.861

0.770

0.851

0.761

0.805

0.660

0.724

0.697

0.863

0.854

0.861

0.858

0.855

0.867

0.862

0.867

a

Standardized Cronbach’s a. The short form of the MSSE consisted of the 10 boldface items.

b

express your needs or ideas’’, ‘‘you can write clearly so that others can read what you wrote’’, and ‘‘you can go on a trip that keeps you away from home the whole day’’. The wording of some items looks similar, for example, ‘‘you can control your fatigue’’ versus ‘‘you can decrease your fatigue quite a bit’’, and ‘‘you can deal with the frustration of MS’’ versus ‘‘you can deal with the uncertainty of MS’’. In addition, the MI values of the above items were high. Such reasons supported our decisions to delete 8 items. The remaining 10 items have high factor loadings on one of the two factors, indicating each item interprets its reflected factor specifically and sufficiently. Construct validity We have thoroughly examined the construct validity of the 18-itm MSSE and MSSE-10, which are, with increasing generality, MS symptoms, dysfunction, disability, psychosocial aspects, mental and emotional well-being, and quality of life. The Control

subscale of the MSSE-10 had stronger correlations with all used measures than did the Function subscale. Such results may be because there were only 4 items in the Function subscale while there were 6 items in the Control subscale. In addition, the preserved 4 items of the Function subscale were more specific, complex activities of daily living, for example, taking steps on uneven ground, getting dressed or undressed, getting in and out of a vehicle, and taking a bath. These 4 items required advanced motor planning, balance, and transition. Therefore, legitimately, they correlated more strongly with MS symptoms, perceived disability and function, and MS physical impact. In contrast to the Function subscale, the coverage of the Control subscale was broadly involved in symptoms management, reactions to functional limitations, and making adjustments to living with MS. Justifiably, the Control subscale of the original and refined versions would be expected to correlate significantly with all specific and general constructs measured in the present study. More interestingly, the six retained items of the Control

8

C.-Y. Chiu & R. W. Motl

Disabil Rehabil, Early Online: 1–10

Table 5. Correlations between the long and short forms of the MSSE in sample 1 and 2, respectively. Sample 1

LF-Total LF-Function LF-Control SF-Total SF-Function SF-Control

LFtotal

LFfunction

– 0.83* 0.96* 0.97* 0.62* 0.94*

– 0.63* 0.77* 0.85* 0.63*

LFcontrol

– 0.95* 0.42* 0.98*

Sample 2

SFtotal

SFfunction

– 0.64* 0.97*

SFcontrol

LFtotal

LFfunction

LFcontrol

SFtotal

SFfunction

SFcontrol

–

– 0.85* 0.95* 0.97* 0.63* 0.93*

– 0.64* 0.80* 0.87* 0.63*

– 0.93* 0.39* 0.97*

– 0.64* 0.96*

– 0.39*

–

– 0.43*

LF, long form; SF, short form. *Correlation is significant at the 0.0001 level.

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Table 6. Correlations between the long form and short form of the MSSE and construct relevant measures in sample 1. Long form* Construct Measures Symptom, dysfunction, disability Symptom inventory SF-McGill Pain Questionnaire Fatigue Severity Scale LLFDI-overall function LLFDI-disability-limitation LLFDI-disability-frequency PDDSa Psychosocial aspects Exercise Self-Efficacy Scale Social Provisions Scale-Total Mental/emotional well-being HADS-Depression HADS-Anxiety SWLS Quality of life SF-12 PCS SF-12 MCS MSIS-29-Physical MSIS-29-Psychological Leeds MS quality of life Scale

Short form*

Total

Function

Control

Total

Function

Control

0.65 0.48 0.58 0.66 0.73 0.51 0.55

0.62 0.36 0.37 0.67 0.60 0.42 0.50

0.59 0.48 0.61 0.57 0.69 0.50 0.50

0.60 0.47 0.54 0.61 0.69 0.50 0.51

0.43 0.28 0.21 0.50 0.41 0.27 0.32

0.56 0.46 0.57 0.56 0.68 0.50 0.50

0.52 0.45

0.47 0.35

0.47 0.44

0.48 0.46

0.32 0.26

0.47 0.46

0.62 0.39 0.56

0.42 0.25 0.40

0.65 0.42 0.57

0.62 0.39 0.57

0.25 0.18 0.28

0.64 0.41 0.58

0.60 0.43 0.73 0.64 0.64

0.54 0.23 0.67 0.49 0.45

0.56 0.48 0.67 0.63 0.66

0.57 0.41 0.69 0.62 0.64

0.37 0.13 0.49 0.35 0.33

0.55 0.44 0.65 0.62 0.64

SF-McGill Pain Questionnaire, the short-form McGill Pain Questionnaire; LLFDI, late-life function and disability instrument; PDDS, patient determined disease steps scale; HADS, hospital anxiety and depression scale; SWLS, satisfaction with life scale; SF-12 PCS, SF12-physical component summary scale; SF-12 MCS, SF12-mental component summary scale; MSIS-29, multiple sclerosis impact scale. *All correlations are significant at the 0.0001 level. a In sample 2, PDDS was correlated with the long form of the MSSE total score, the MSSE-function subscale score, and the MSSE-Control subscale score at 0.54*, 0.52* and 0.47*, respectively; with the Short Form of the MSSE total score, short form Function and Control subscales at 0.50*, 0.39* and 0.45*, respectively.

subscale correlated with the total score of the MSSE-10 at 0.97 (p50.0001), but at 0.94 with the total score of the 18-item MSSE (p50.0001). We would further recommend that the 6-item Control subscale could be the most parsimonious version for evaluating self-efficacy in MS. The 4-item and 9-item Function subscales had the same highest construct coefficients with the LLFDI-overall function and disability limitation, and the SI. Similarly, the 6-item and 9item Control subscales had the same highest construct coefficients with the LLFDI-overall function and disability limitation, FSS, and SI. The MSSE-10 inherited the relevant constructs of the 18-item MSSE. Although it showed there are no clearly divergent constructs between the measures of symptoms, dysfunction, and disability and the Function and Control subscales, the 6-item Control subscale had evidently higher correlations with these measures than the 4-item Function subscale had.

For the construct validity of psychosocial aspects with the 9-item Function subscale, since many items in this subscale were related to movement capability and physical stamina, it was correlated more strongly with the EXSE than with the SPS. It could be partly because engaging in an exercise behavior among people with MS has multiple challenges in physical function such as overcoming fatigue, symptoms and impaired mobility. In contrast, either the 9-item or 6-item Control subscale was correlated equally strongly with the EXSE and SPS. Social support has been regarded as an important mediator and moderator in the adjustment mechanism of coping with MS [14–18,42,43], but also as a resource to build and maintain selfefficacy [7]. For instance, Bandura postulated four resources to develop an individual’s self-efficacy, which are previous mastery experience (e.g. how well and how often an individual with MS had engaged in exercise), vicarious experiences (e.g. observing or

Self-efficacy in MS

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DOI: 10.3109/09638288.2015.1021022

hearing about others with MS doing exercise), social persuasions (e.g. friends or family members encourage them to do exercise), and somatic and emotional status (e.g. anxiety and depression were related with self-efficacy) [7]. Literally, two of those four resources are associated with social support. For the construct validity of quality of life scales, the 9-item Function and 9-item Control subscales correlated strongly and equally with the SF-12 physical components and the physical subscale of the MSIS-29. However, the 4-item Function subscale relatively highly correlated with the physical subscale of the MSIS-29 than with the SF-12 physical components. The 9-item and 6-item Control subscales had similar strength of correlations with all used scales of quality of life. The measures of MSspecific quality of life (i.e. MSIS-29) have regarded as more sensitive when evaluating the quality of life for people with MS than the general measures of quality of life (i.e. SF-12). This may explain why the 18-item MSSE and the MSSE-10 had stronger correlations with the MSIS-29 than the SF-12. Overall, perceived internal locus of control either measured by the 9-item or 6-item Control subscale has implied its important influences on the quality of life of people with MS. Such internal locus of control has related with autonomous motivation, which has been considered as an important factor to initiate and adherence to self-management of health [44,45]. More importantly, such an internal locus of control has a potential to be an intervention to improve the well-being and quality of life in people with MS. It is noteworthy that the 18-item MSSE has been used as a validity criterion for other existing self-efficacy scales in people with MS. The Multiple Sclerosis Self-Efficacy Scale (MSSS) was coded from a free-association interview which only asked one question about how MS affects individuals’ lives among 15 MS patients [46]. The MSSS had four factors (independence, worries, control, and confidence in social situation) composed of 14 items. The MSSS was correlated strongly with the 18-item MSSE (r ¼ 0.64, p50.01). The MSSS was mainly derived from patients’ concerns with emotional, social, and physical well-being, while the MSSE was based on symptoms, function, and impact on daily living activities. The Unidimensional Self-efficacy Scale (USEMS) was a curtailed scale derivative from a Rasch analysis which pruned off combined items of the MSSS [47] and Liverpool SelfEfficacy Scale [48]. The preserved 12 items had optimal differential item functioning. Although its construct was unidimensional due to the post-hoc Rasch-based test, it may have multiple domains from its original scales, including control, personal agency, and independence domains. The USE-MS was highly correlated with the MSSE (r ¼ 0.66, p50.05) [47]. Young et al. validated the USE-MS in the United Kingdom and suggested that the USE-MS needs to be validated in different cultural contexts [47]. According to the above studies of other MS self-efficacy scales, the 18-item MSSE has been all-inclusive and robust when those other scales were developed. We further validated MSSE-10 which has concise items but contains comprehensive constructs of managing and coping with MS. Limitations We recognized limitations of the present study and provided suggestions for future research. We mainly recruited females with RRMS. All participants were able to walk. Therefore, the scale statistical analysis was valid only in this particular sample of MS subjects and could not be generalized among other clinical courses of MS or in those with severe disability. The majority of participants were Caucasians, married, and had fair well income and education. In order to improve generalizability, the future studies may like to include other courses of MS, increasing the number of males and other races/ethnicities, and recruiting people

9

with MS who have disadvantaged social-economic status. By doing so, bias will be reduced to some extent because selfefficacy has been correlated with social-economic status and health conditions, and also because coping styles are different between genders [7,49]. Additionally, the future study may like to recruit people who have severer disability. This could provide a chance to examine the sensitivity and generalizability of the MSSE and its ceiling or floor effects. We used one statistic method (i.e. SEM) to improve the construct validity and to shorten a large amount of items. Additional research is warranted to further examine the MSSE-10 by CFA, and, in particular, with other psychometric analyses, such as Rasch model analysis. This will confirm and possibly improve the metric quality. In addition, we collected criteria measures and the 18-item MSSE at the same time, which may be at risk of raising excess response set variance. It is possible to overestimate some already weak external validity correlations.

Conclusions Overall, the MSSE-10 has good psychometrics, namely, two valid factors, high construct validity with several bio-psycho-social aspects, and high internal consistency. The present study has confirmed an effective scale specifically measuring MS-specific self-efficacy, the 10-item MSSE. Additionally, we suggested that the preserved 6 items of the MSSE-Control subscale could be another even shorter but also valid instrument for evaluating selfefficacy in coping with MS. Both the 10-item MSSE and 6-item Control subscale could be employed in clinical practice and survey research effectively and efficiently.

Declaration of interest This investigation was supported, in part, by the United States Department of Health and Human Services, National Institutes of Health, National Institute of Neurological Diseases and Stroke (Grant NS054050). This research was further supported, in part, by a grant from the National Multiple Sclerosis Society (RG# 3926A2/1).

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