Capture-recapture method to determine the best design of a surveillance system. Application to a thyroid cancer registry.

The capture-recapture method is often confronted, when assessing completeness of surveys, to problems of dependence of data sources. The objective of this paper is to discuss the application of capture-recapture methods to choose the optimal combination of sources for a surveillance system. Our approach is based on: (1) using multiple sources, (2) assessing dependence between sources and between pools of dependent sources and other sources, (3) ruling out combinations that yield biased estimates, and (4) choosing the combinations of sources that have the best ratio between precision and applicability. We studied the independence for each pair of sources by computing the capture-recapture odds ratio. We characterized all combinations of sources by their sensitivity, coefficient of variation of the estimated number of cases, and level of resources needed to ascertain cases. Application of the approach is illustrated by data from a survey of thyroid cancer in New Caledonia, where five sources were used to estimate the incidence. The five sources provided 119 cases; the exhaustivity of sources and combinations of sources varied from 27.1 to 99.2%. Determination of dependence revealed ten dependencies out of 22 combinations. Coefficients of variation of the estimated number of cases varied from 0.83 to 27.79. The preferred combination included four sources and had a sensitivity of 97.5 and a coefficient of variation of 0.94. An assessment of dependence, based on simple criteria, can be used to choose the best combination of sources for a registry or a surveillance system.