Validity and reliability of the Sri Lankan version of the kidney disease quality of life questionnaire (KDQOL-SF™)

BACKGROUND The disabling symptoms, various food and fluid restrictions, restrictions to social life and stigma and taboos attached to Chronic Kidney Disease (CKD), have shown to pose a significant bearing on a patient's Quality of Life (QOL). In the present study the Kidney Disease QOL-Short Form (KDQOL-SF™) was culturally adapted, modified and translated into Sinhala and validity and reliability were assessed. METHOD The process to culturally adapt the Kidney Disease Specific Component (KDSC) of KDQOL-SF™ was carried out by the modified Delphi process with a group of experts. The construct validity of the KDSC was assessed using Exploratory Factor Analysis (EFA). Appraising construct validity of SF-36 component of KDQOL-SF™ was done by assessing the convergent and discriminant validity using the Multitrait-Multimethod Matrix technique (MTMM). Randomly selected 250 CKD patients attending the five renal clinics in Polonnauwa were used to assess the construct validity. To assess the test-retest reliability of the instrument, within a period of one week, 30 randomly selected study participants were visited at their households. RESULTS Two hundred and fifty adults with documented evidence of CKD participated. The EFA carried out using principal component factoring method and rotated by Varimax orthogonal method resulted in 14 factors with Eigen values ranging from 1.062-8.746. This 14 factor model explained 84.1% of total variance of the initial system. The communalities extracted for domains were all close to one. All the items were loaded to one or more domains with factor coefficients of more than 0.4, not requiring any of the items to be dropped. Few items which showed similarly high factor coefficients in more than one factor were assigned to a factor ensuring the pattern in the theoretical framework of the questionnaire based on expert opinion and vigorous analysis of literature. Convergent and divergent validity assessed using MTMM, revealed satisfactory construct validity. Cronbach's alpha of all domains of KDQOL-SF™ except for cognitive function and Social function, exceeded Nunnally's criteria of 0.7. The Intra class Correlation Coefficients (ICC) were more than 0.8 for all the domains, which indicated good test re-test reliability. CONCLUSIONS KDQOL-SF™ is a valid and reliable instrument which can be used to assess QOL of CKD patients in Sri Lanka.