A method to determine if consenters to population surveys are representative of the target study population

Background Searching medical records of study non-responders to investigate selection bias is no longer acceptable. We explore an alternative by comparing consultation rates in survey responders who consented to medical record review, with anonymized consultation rates for the total practice populations. Methods Anonymized aggregated consultation rates for the year following a population-based survey were calculated for headache and a number of other conditions (chosen to reflect a mixture of chronic and episodic conditions). These rates were compared across two groups of adults: (i) respond-ers to the survey who consented to medical record review and (ii) a 'population group' created from records of the general practices participating in the survey to represent all patients aged 18 years and over at the mid-point in the study year. The consultation rates for the conditions were compared across the two groups using direct standardization. Results Adjusted consultation rates were similar but generally higher in the responders. Conclusions This alternative method applied here offers one potential approach to determine whether study respondents are representative of the population from which they were sampled with respect to general practice consultations.