Keywords: Arabic version, Psoriasis Disability Index, psoriasis

Transcription

1 Original article 143 Reliability and validity of the Arabic version of the Psoriasis Disability Index questionnaire Hatem M. Zedan a, Hisham D. Gaber a, Ahmed K. Ibrahim b and Ereny Z. Refaa a Departments of a Dermatology, Venereology and Andrology and b Community Medicine, Faculty of Medicine, Assiut University, Assiut, Egypt Correspondence to Hisham D. Gaber, MD, Department of Dermatology, Venereology and Andrology, Faculty of Medicine, Assiut University, Assiut 17515, Egypt Tel: ; fax: ; hishamdiabg@hotmail.com Received 30 March 2016 Accepted 12 June 2016 Journal of the Egyptian Women s Dermatologic Society 2016, 13: Background Psoriasis has a significant negative impact on patients quality of life. Psoriasis Disability Index (PDI) is a psoriasis-specific questionnaire that was developed by Finlay and Coles, which concerns the functional lifestyle disabilities caused by psoriasis. It has been used internationally for almost 20 years and has been translated into at least 26 languages. Objective The objective of this study was to evaluate the reliability and validity of the Arabic version of the PDI questionnaire for Egyptian psoriasis patients. Patients and methods One hundred adult Egyptian patients with chronic plaque-type psoriasis aged 16 years or older with no other systemic disease were enrolled in this study. The patients were examined to determine the clinical type of psoriasis and to measure the severity of psoriasis by calculating Psoriasis Area Severity Index score. The impact of psoriasis on quality of life was assessed using the Arabic version of the PDI after translation and cultural adaptation according to WHO guidelines. Results The internal consistency for the 15 items of the Arabic version of the PDI questionnaire was significant; intraclass correlation coefficient was and Cronbach s a coefficient was 0.860, indicating reliability of the developed Arabic version. Conclusion The Arabic version of the PDI questionnaire was found to be a reliable and valid measure for evaluating the quality of life for Egyptian patients with psoriasis. Keywords: Arabic version, Psoriasis Disability Index, psoriasis J Egypt Women Dermatol Soc 13: & 2016 Egyptian Women s Dermatologic Society Introduction Quality of life (QOL) is a broad multidimensional concept that usually includes subjective evaluation of both positive and negative aspects of life [1]. A number of factors contribute to this sense of well-being, including a good health, a secure social and occupational environment, financial security, spirituality, self-confidence and strong, supportive relationships [2]. A major problem with QOL measures is that there is a lack of standardization in definitions, conceptualizations, and psychometric testing [3]. QOL is usually assessed by using standardized and validated questionnaires [4]. Psoriasis can be measured using objective measures of the extent and severity of the skin disease, but these measures do not capture the impact of the disease on patients lives. Various tools can be used to assess psoriasis severity and QOL together [5]. This study was presented as an oral presentation at the ESVD Derma Cairo ( ); Cairo, Egypt; The Psoriasis Disability Index (PDI) is a psoriasis-specific questionnaire that was developed by Finlay and Coles [6], and it concerns the functional lifestyle disabilities caused by psoriasis. It has been used internationally for almost 20 years [7] and has been translated into at least 26 languages [8]. PDI is a 15-item scale. It includes areas of daily activities, personal relationship, work or school, leisure, and treatment [9]. All items are rated on a four-point scale, with responses of not at all, a little, a lot, and very much scored 0, 1, 2, and 3, respectively. Item scores are summed to yield a total score (range: 0 45), with higher score indicating greater limitations caused by psoriasis [10]. The impact of psoriasis on patients overall QOL is broad and deep, including effects on emotional well-being, psychological stress, relationships, work, social activities, financial burden, and even physical function [11]. The aim of this study was to translate and adapt the PDI to Arabic language and to use this Arabic version in the study of QOL in a group of psoriatic patients in Upper & 2016 Egyptian Women s Dermatologic Society DOI: /01.EWX c

2 144 Journal of the Egyptian Women s Dermatologic Society Egypt to provide the reliability and validity of this new version. Patients and methods The study is a cross-sectional study. One hundred adult Egyptian patients with chronic plaque-type psoriasis aged 16 years or older with no other systemic disease were recruited from Dermatology Department, Assiut University Hospital, in the period from December 2014 to September Verbal consent to participate was fulfilled after a brief description of the nature and objectives of the study to each patient. A detailed personal history was taken from all patients, including name of the patient, age, sex, residence, marital state, and special habits such as smoking. Next, the patients were examined to determine the clinical type of psoriasis and to measure the severity of psoriasis by calculating Psoriasis Area Severity Index (PASI) score. The impact of psoriasis on QOL was assessed using the Arabic version of the PDI. Translation of the questionnaire First of all, we have taken a formal permission from the original author Professor Andrew Finlay, on 30 April 2014, to translate the original version of the PDI questionnaire into Arabic language and to validate this Arabic version. Next, we have followed the WHO guidelines for scale development and translation, as follows [12]: Forward translation Two expert translators in the Center of Translation and Linguistic Research, Assiut University, produced independent Arabic-language translations of the English version of the PDI questionnaire; the translated version has been reviewed by a committee of experts from both Center of Translation and Linguistic Research and Dermatology Department, Assiut University Hospital, who developed a unique Arabic-language translation and modified some items to make it more applicable and culturally appropriate. Some changes were made for example, hairdresser was substituted for shaver/hairdresser and partner was substituted for husband/wife. Expert panel back-translation A back-translation (from Arabic to English) was performed by other two expert translators from the International Center of Translation to verify that the original questionnaire could be reinstated without any major modification and without alteration of the original ideas and items. Both the final forward and backward translations were submitted to the developer of the original questionnaire Professor Finlay for review and comments, and he agreed and approved our Arabic translation and published it on his site at Cardiff University website in December Pretesting and cognitive interviewing Qualitative pretesting of the revised Arabic version of the PDI was carried out with 20 psoriasis patients from the Outpatient Dermatology Clinic, Assiut University Hospital, using an interview technique to determine whether each question was correctly understood. Patients were asked to justify their answers and explain what the questions meant in their own words. They expressed their well-understanding for each item of the Arabic version of the PDI. Final Arabic version Several indicators for reliability and validity were proven for our Arabic version. Scale distribution was evaluated by calculating the observed range of scores using skewness and kurtosis. Internal consistency of the scale was assessed using item analysis, and Cronbach s a coefficient factor was calculated for the total scale. Intraclass correlation coefficient (ICC) was used, which is an important indicator for both reliability and validity. The discriminant validity is an important indicator for construct validity, and it was measured using Ferguson s d factor. Confirmatory factor analysis (CFA) was conducted to confirm the separate factors within the scale. Convergent validity was tested by examining the extent to which scores on the PDI demonstrated logical relationships with the PASI score, age, marital status, occupation, and smoking. Correlations were calculated using Spearman s rank correlation coefficient. Statistical analysis Data were verified, coded by the researcher, and analyzed using SPSS (version 21; SPSS Inc., Chicago, Illinois, USA). Descriptive statistics means, SDs, medians, interquartile range, and percentages were calculated. Test of significances, w 2 -test, was used to compare the difference in distribution of frequencies among different groups. For continuous variables, independent t-test analysis was carried out to compare the means of normally distributed data, whereas Mann Whitney U-test was calculated to test the median differences of the data that do not follow normal distribution. Correlation analysis was used to test the association between variables (Spearman s rank correlation). Item analysis was performed, and Cronbach s a and ICC were calculated for total PDI and for separate items. A P-value was considered significant when it was less than or equal to Results The study included 100 patients with chronic plaque psoriasis who had received the Arabic version of PDI and completed all the questions. The demographic data of these patients are shown in Table 1.

3 Arabic version of the Psoriasis Disability Index Zedan et al. 145 Table 1. Sociodemographic data of the studied sample Variables Category N (%) (N = 100) Age (years) Mean ± SD 39.5 ± 16.9 Median (range) 37 (16 80) Sex Male 58 (58) Female 42 (42) Marital status Not married 38 (38) Married 62 (62) Residence Assiut 80 (80) Outside Assiut 20 (20) Smoking Nonsmoker 63 (87) Smoker 37 (37) Occupation Unemployed 48 (48) Employed 52 (52) PASI Mean ± SD 4.5 ± 2.9 Median (range) 3.9 ( ) Total PDI score Mean ± SD 23.9 ± 8.3 Median (range) 24 (4 40) PASI, Psoriasis Area Severity Index; PDI, Psoriasis Disability Index. The Psoriasis Disability Index score according to sociodemographic data The studied sample showed that there was a significant difference in both PASI and PDI scores between married and single patients (P = and 0.032, respectively). In addition, PDI showed a significant different score between smokers and nonsmokers (P = 0.001). On the other hand, it showed that there was no statistically significant relation for either PASI or PDI scores with different age and sex groups (P = and for age and and for sex, respectively). In addition, there was no significant difference between patients at regular work or school and patients not at regular work in both PDI and PASI scores (P = and 0.155). The PDI also showed that there was no significant difference between patients with mild psoriasis and those with moderate disease (P = 0.06), as shown in Table 2 (Figs 1 5). Table 2. Psoriasis Area Severity Index score and Psoriasis Disability Index score differences of the studied sample according to their sociodemographic characteristics Mean ± SD Variables PASI score PDI score Marital status Single 3.5 ± ± 8.5 Married 5.2 ± ± 7.9 P-value 0.007* 0.032* Smoking status Nonsmoker 4.3 ± ± 7.9 Smoker 4.9 ± ± 7.7 P-value * Age (years) o ± ± 9.6 Z ± ± 6.6 P-value Sex Male 4.8 ± ± 8.7 Female 4.2 ± ± 7.5 P-value Occupation Unemployed 5.0 ± ± 7.2 Employed/at school 4.3 ± ± 8.8 P-value PASI category Mild (o7) 23.2 ± 8.4 Moderate (Z7) 26.9 ± 7.2 P-value PASI, Psoriasis Area Severity Index; PDI, Psoriasis Disability Index. *Po0.05 is considered statistically significant. Figure 1. Study distribution PDI ranged from 4 to 40, with the mean of ± 8.3 and 95% confidence interval of ). The scores were normally distributed (skewness = 0.09 and kurtosis = 0.50) (i.e. the curve of distribution is not shifted to left or right sides) (Fig. 6). Reliability was detected here by Cronbach s a coefficient factor, which is equal to (normally, Cronbach s a >0.7 is highly reliable). The discrimination value, which is the ability to discriminate between variables and is an important indicator for validity, measured by Ferguson s d was (normally, Ferguson s d >0.5 is valid). Scale reliability ICC measures the ability of each question to represent the questionnaire. It is an important indicator for both reliability and validity. Results of item-total correlation for each question more than 0.3 (in psychometric measures) is considered significant. The internal consistency for the 15-item of the Arabic version of the PDI questionnaire was significant ICC was and Cronbach s a coefficient was indicating reliability of the developed Arabic version. Distribution of the Psoriasis Area Severity Index score among the studied sample. Item-total correlation of questions 6a and 7a is less than 0.3 (0.141and 0.262, respectively). This means that if we remove these questions the questionnaire will not be affected. Cronbach s a coefficient factor in Table 4 is 0.86 despite its result in Table 3 being equal to This difference occurs because the measurement of Cronbach s a during measurement of internal consistency is based on standardized items only, and thus factors less than 0.3 are suppressed before calculation of Cronbach s a coefficient factor (Figs 7 and 8).

4 146 Journal of the Egyptian Women s Dermatologic Society Figure 2. Figure 4. Box plot of the Psoriasis Area Severity Index (PASI) and Psoriasis Disability Index (PDI) scores according to marital status. Box plot of the Psoriasis Area Severity Index (PASI) and Psoriasis Disability Index (PDI) scores according to smoking status. Figure 3. Figure 5. Box plot of the Psoriasis Area Severity Index (PASI) and Psoriasis Disability Index (PDI) scores according to occupation. Box plot of the Psoriasis Disability Index (PDI) scores according to Psoriasis Area Severity Index (PASI) categories. Confirmatory factor analysis CFA was conducted to confirm the separate factors within the scale. Each factor was judged according to its power to explain variation between participants. Factor analysis was conducted for all 15 items. The first factor (factor I), which is the physical and functional factor and which includes 11 items, can explain 34.2% of the variance; the second factor (factor II), which is the social and sexual factor and which includes four items, can explain 18.9% of the variance, as shown in Table 5 and Fig. 4. This means that the questions on factors I and II can represent the questionnaire by 53.1%. Discussion Psoriasis is a common chronic inflammatory skin disorder that affects 2 4% of the general population [13]. It represents about 0.19% in Egypt [14]. It is generally considered as a genetic disease that can be influenced by numerous environmental factors [15]. Psoriasis has a significant negative impact on patients QOL. Many factors may contribute to this lower QOL: the chronic nature of the disease, the lack of control over unexpected outbreaks of the symptoms, and from other reactions to the disease [16]. Various tools can be used to

5 Arabic version of the Psoriasis Disability Index Zedan et al. 147 Figure 6. equally affected by psoriasis with regard to their QOL. Therefore, we found that there was no difference between working (most of them are male) and nonworking (most of them are female) patients. However, married patients were found to be more affected than single Table 3. Statistical properties of the Psoriasis Disability Index scale Parameters Data Mean ± SD ± % confidence interval for mean % trimmed mean Median 24 Range 4 40 Interquartile range 12 Skewness 0.09 Kurtosis 0.50 Reliability (Cronbach s a) Discrimination (Ferguson s d) Distribution of the Psoriasis Disability Index (PDI) score among the studied sample (normal distribution). assess psoriasis severity and Health Related Quality Of Life together. These measures are classified as psoriasis specific, skin specific, generic, and mixed [5]. The present study was concerned with translation and validation of an Arabic version of the PDI, which is an important psoriasis-specific measure for QOL that was developed by Finlay and Coles [6] and has been translated into at least 26 languages [8]. The Arabic version was easily understood and answered by the patients. Face and content validity were assessed as satisfactory. The PDI seems to capture issues of importance to patients as was found in the Norwegian version [17]. Concurrent validity was assessed as follows: the mean of the PDI score in the current study was 23.9 ± 2.9 (range: 4 40), nearly equal to the mean PDI score of a previous study in Upper Egypt, which was 20.4 ± 6.8 (range: 3 38) [18]. However, it was higher than that measured in the English version in USA, which was 7.3 ± 7.2 [9], and in the Chinese patient, which was 12.8 ± 9.4 [10]. In the Amsterdam systematic study of the QOL in patients with psoriasis, the mean overall PDI scores ranged from 16.5 to 44 [19]. However, it was lower than that of Iran, which was 28 ± [20]. This reflects the relatively more sensitive aspect of the social distress in our community, which was noted previously by Zedan et al. [18]. In our study, there was a significant difference in both PASI and PDI scores between married and single patients. In addition, PDI showed a significant different score between smokers and nonsmokers. In addition, there was no significant difference between patients at regular work or school and patients not at regular work in both PDI and PASI scores. This can be explained by the fact that 27 patients from the 32 unemployed patients were housewives and most of them were married. Therefore, collectively men and women are Table 4. Internal consistency of the Psoriasis Disability Index scale 15 items Questions Symptom Q1 How much has your psoriasis interfered with you carrying out work around the house or garden? Q2 How often have you worn different types or colors of clothes because of your psoriasis? Q3 How much more have you had to change or wash your clothes? Q4 How much of a problem has your psoriasis been at the hairdressers? Q5 How much has your psoriasis resulted in you having to take more baths than usual? Q6 How much has your psoriasis made you lose time off work or school? Q6a How much has your psoriasis stopped you carrying out your normal daily activities? Q7 How much has your psoriasis prevented you from doing things at work or school? Q7a How much has your psoriasis altered the way in which you carry out your normal daily activities? Q8 Has your career been affected by your psoriasis? Q8a Has your career been affected by your psoriasis? Q9 Has your psoriasis resulted in sexual difficulties? Q10 Has your psoriasis created problems with your partner or any of your close friends or relatives? Q11 How much has your psoriasis stopped you going out socially or to any special functions? Q12 Is your psoriasis making it difficult for you to do any sport? Q13 Have you been unable to use, criticized, or stopped from using communal bathing or changing facilities? Q14 Has your psoriasis resulted in you smoking or drinking alcohol more than you would do normally? Q15 To what extent has your psoriasis or treatment made your home messy? Cronbach s a based on standardized item = ICC (95% ( ) CI)** **Less than 0.3 considered to be low item-total correlation. CI, confidence interval; ICC, intraclass correlation coefficient. Item-total correlation

6 148 Journal of the Egyptian Women s Dermatologic Society Figure 7. patients, and also smokers were found to be more affected with regard to their QOL by psoriasis compared with nonsmokers. There is no difference in the severity of physical symptoms suffered by men and women. However, women and men have different subjective perceptions of how symptoms affect their social interactions, emotional states, and, ultimately, their QOL [21]. Confirmatory factor analysis scree plot using principal component analysis. Figure 8. Aghaei et al. [20] found that the PDI values were higher in men than in women, and in unmarried than in married patients. Their explanation was that all the female patients were housekeepers and not at regular work. In addition, some of their patients had a few problems with questions 9 and 10 because of cultural differences and shame of talking about sexual relationships. However, in our study the interviewer was a female doctor, so we could reach more to our female patients and have a chance to find the real answers for our questionnaire away from shamefulness. On the other hand, the mean PDI score among mild PASI was lower than the mean PDI score among moderate PASI, but it cannot reach the statistically significant difference; this may be because of the sample size. This has been previously noted by Wall et al. [22]. Korte et al. [19] found that the association between QOL and disease severity and disability differ greatly between the clinical assessment and the patient assessment of their psoriasis. Therefore, the patient s view regarding his disease severity should be kept in mind while dealing with the patient and making treatment decision. Correlation between Psoriasis Disability Index (PDI) score and Psoriasis Area Severity Index (PASI) score. The internal consistency for the 15 items of the developed Arabic version of the PDI was good; ICC equals 0.85 (range: ) and Cronbach s a was 0.86 based on standardized items. This reflects its usefulness and its adequate internal consistency to discriminate different domains of the patient s QOL. In Persian version, ICC ranged from 0.72 to 1.00 and Cronbach s a was 0.92 [20]. In the Chinese version, Table 5. Loading from direct oblimin rotation matrix (N = 100) Factor a Questions I II Q1: How much has your psoriasis interfered with you carrying out work around the house or garden? Q2: How often have you worn different types or colors of clothes because of your psoriasis? Q3: How much more have you had to change or wash your clothes? Q4: How much of a problem has your psoriasis been at the hairdressers? Q5: How much has your psoriasis resulted in you having to take more baths than usual? Q6: How much has your psoriasis made you lose time off work or school? Q7: How much has your psoriasis prevented you from doing things at work or school? Q8: Has your career been affected by your psoriasis? Q9: Has your psoriasis resulted in sexual difficulties? Q10: Has your psoriasis created problems with your partner or any of your close friends or relatives? Q11: How much has your psoriasis stopped you going out socially or to any special functions? Q12: Is your psoriasis making it difficult for you to do any sport? Q13: Have you been unable to use, criticized or stopped from using communal bathing or changing facilities? Q14: Has your psoriasis resulted in you smoking or drinking alcohol more than you would do normally? Q15: To what extent has your psoriasis or treatment made your home messy? %Variance a Factor loadingso0.4 were suppressed.

7 Arabic version of the Psoriasis Disability Index Zedan et al. 149 Cronbach s a was 0.91 [10]. In the Spanish version, the internal consistency measured by Cronbach s a was 0.89 [23]. During the analysis of the Arabic version, the results of CFA scree plot using principle component analysis confirmed that the main scale domain has a leveling off of eigenvalues after the first and second factors (factors I and II), suggesting that the questionnaire should be of two main domains that can explain 53.1% of the variance. The first factor (factor I), which is the physical and functional factor that includes 11 items, can explain 34.2% of the variance. The second factor (factor II), which is the social and sexual factor and which includes four items, can explain 18.9% of the variance. In the Persian version, the principal component analysis was performed and a three-factor structure was loaded, producing the factors of physical, social, and sexual dysfunction [20]. In addition, in the Norwegian version, it has been observed that three factors labeled physical, social, and hygienic disabilities, respectively, could underlie the disabilities of psoriasis using the PDI [17]. The Chinese version of PDI confirmed the two-factor conception of the PDI, one concerning work-related disabilities and the other concerning hygiene and embarrassment [10]. There was an association between PDI and PASI scores, which means that a higher PASI score was associated with a high PDI score. The significant positive correlation between the degree of disability attributed to psoriasis measured by the PDI with the extent and severity of the disease is in agreement with the results of Ramsay and O Reagan [24] and Finlay and Coles [6]. In the Persian version, there was no correlation between the mean PDI with the mean PASI in the patients with skin lesions on skin areas covered by clothes. In the patients with lesions on visible exposed skin areas (such as face and distal extremities), the correlation was statistically significant. The correlation coefficients ranged between the minimum of 0.42 obtained for work and study and personal relationships and the maximum of 0.80 for personal relationship and treatment, being, in most of the cases, acceptable [20]. In the Chinese version, the PDI score increased significantly with the increasing severity of psoriasis. The results of known groups comparison indicated that the discriminate ability of the PDI was good enough to distinguish the patients with different severities of psoriasis, which was consistent with previous studies [10]. In the US study, the total PDI score increased significantly with increasing problems in everyday life score. In addition, the PDI was significantly related to extent of disease [9]. Also, the Spanish version found that the PDI score was correlated with the PASI scores [23]. In one qualitative study carried out to assess the determinants of QOL in the US population with psoriasis, body surface area showed the strongest association with decrements in QOL, among other factors including patients age, sex, income, duration of psoriasis, and number of physicians seen in the past 2 years [16]. However, there are other studies that have indicated an inverse relationship between QOL and severity of psoriasis [25]. Conclusion The Arabic version of the PDI questionnaire was found to be a reliable and valid measure for evaluating the QOL for Egyptian patients with psoriasis. Acknowledgements Conflicts of interest There are no conflicts of interest. References 1 Centers for Disease Control and Prevention (CDC). Measuring healthy days: population assessment of health-related quality of life. Atlanta: CDC; Juniper EF, Guyatt GH, Streiner DL, King DR. Clinical impact versus factor analysis for quality of life questionnaire construction. 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