Estimating the rate of non-participation and its influence on the study results: Sankara Nethralaya Diabetic Retinopathy Epidemiology and Molecular Genetics Study report 32.

PURPOSE To report the non-participation rates in a cross-sectional study, compare participants with non-participants, elucidate barriers for non-response and evaluate the influence of non-responders on the outcome measure. METHODS The Sankara Nethralaya Diabetic Retinopathy Epidemiology and Molecular Genetics Study had 2 steps in which non- participation was possible. Step 1 was an estimation of fasting blood sugar at the participants' homes, and step 2 a base hospital examination. The sociodemographic information was collected at the time of enumeration. The barriers against participation were noted at refusal. The data of the participants were compared with the urban Tamil Nadu population data from the 2001 census. RESULTS The non-participation rate was 3.6% in the field (step 1), and 13.9% at the base hospital (step 2). At step 1, older men and unemployed women had a lesser odds ratio for non-participation than younger age groups. At step 2, employment was significant for non-participation in men, and age between 50 and 59 years, illiteracy and unemployment in women. CONCLUSION The barriers against participation differed between steps 1 and 2. The study participants were similar to the population of urban Tamil Nadu. Hence, the results of the study can be generalized to the urban Indian population.