Do estimates of intervention coverage obtained from children at immunization clinics provide a reasonable approximation to population values?
OBJECTIVE: The purpose of this study was to determine whether the magnitude of selection bias incurred by measuring child survival intervention coverage at convenient sampling opportunities (child immunization contacts) is sufficiently small for the approach to be used as a management tool within country programs. METHODS: We estimated the magnitude of selection bias by calculating values of 13 health indicators for 31 countries using Demographic and Health Survey data for children immunized with the third dose of the diphtheria-pertussis-tetanus vaccine (DPT3) and those who were immunized with measles vaccine- and comparing their values to those obtained for the population as a whole. RESULTS: Estimates of intervention coverage derived from immunized children are close to population values if immunization coverage exceeds 60%. Levels of bias were lower for interventions that were not delivered directly by formal health services- such as use of mosquito nets among children and provision of more fluid for diarrhea. Levels of bias were also lower when using results for measles vaccine than for DPT3- suggesting that the measles vaccination contact may be the most opportune time to collect data on additional health indicators. CONCLUSIONS: The coverage of immunization programs has reached 60% in 85% of African countries- so selection bias does not appear to invalidate the measurement of intervention coverage at immunization contacts.