Concordance of survey and billing data in a study of outpatient healthcare cost and utilization among epilepsy patients.

We assessed the concordance between healthcare utilization and cost measured with patient survey and billing data among 226 epilepsy patients in a large multi-specialty group practice. Does survey information on utilization combined with prices, provide a cost of care that is approximately equal to the cost of care derived from billing data, utilizing the same price structure? Do measures of cost from survey and billing data yield the same correlates of cost among epilepsy patients? If so, survey data may be utilized to estimate correlates and cost of epilepsy care in cases where complete billing information is not available. For five of eight outpatient services, the concordance coefficients exceeded the practical cut-off value for clinical studies, suggesting substantial agreement between the billing and survey data. Cost was higher when computed from billing data, but the overall concordance (.75) between the cost estimates is relatively high, and comparable to findings in studies on other types of patients. The average 6-month outpatient cost difference was $11 between the two sources of cost estimates. Correlates of cost were similar, whether cost was measured with survey or billing data. The results suggest that correlates of cost and cost estimates derived from survey data may yield similar findings to cost estimates from billing data for policy related studies of epilepsy patients.