Psychometric evaluation of the National Kidney Dialysis and Kidney Transplantation Study symptom checklist: reliability and validity.

BACKGROUND Patient-reported outcomes (PROs) are critical in the evaluation of treatment effectiveness. The National Kidney Dialysis and Kidney Transplantation Study (NKDKTS) symptom checklist was developed in the 1980s as a means to better understand the relationships amongst end-stage renal disease (ESRD), anaemia symptoms and multiple quality of life indicators. Unfortunately, key components of validity and reliability were not established at the time of the study. The present study helps fill this void by evaluating the psychometric properties of the 13-item NKDKTS symptom checklist, a measure of anaemia symptom frequency, in a dialysis population. METHODS The NKDKTS symptom checklist was administered to 104 dialysis patients in three dialysis units at baseline, 48 h and 7 days. Internal consistency, test-retest reliability and construct validity via known-groups responsiveness were evaluated. RESULTS Principal components factor analyses produced a single factor at each time point, with all items loading >0.50 across time points, and accounting for 37%, 44% and 46% of the variance at each time point (respectively). Forcing a 2-factor solution across time points yielded a single instance of an item loading more highly on factor 2 (0.57) than on factor 1 (0.53). Internal consistency was good at all three time points (Cronbach's alpha = 0.86, 0.89 and 0.90, respectively). Known-groups validity was evaluated by examining the symptom scores of subjects categorized by haemoglobin level. Subjects with lower haemoglobin levels reported significantly more symptoms, and the point estimates and variance at each haemoglobin level were stable over time. CONCLUSION The results of this study provide further evidence supporting the validity and reliability of the NKDKTS symptom checklist.