Accuracy of alternative approaches to capture-recapture estimates of disease frequency: Internal validity analysis of data from five sources

The authors used "internal validity analysis" to evaluate the performance o f various capture-recapture methods. Data from studies with five overlappin g, incomplete lists generated subgroups whose known sizes were compared wit h estimates derived from various four-source capture-recapture analyses. In 15 data sets unanalyzed previously (five subgroups of each of three new st udies), the authors observed a trend toward mean underestimation of the kno wn population size by 16-25%. (Coverage of the 90% confidence intervals ass ociated with the method found to be optimal was acceptable (13/15), despite the downward bias.) The authors conjectured that (with the obvious excepti on of geographically disparate lists) most data sets used by epidemiologist s tend to have a net positive dependence; that is, cases captured by one so urce are more likely to be captured by some other available source than are cases selected randomly from the population, and this trend results in a b ias toward underestimation. Attempts to ensure that the underlying assumpti ons of the methods are met, such as minimizing (or adjusting adequately) fo r the possibility of loss due to death or migration, as was undertaken in o ne exceptional study, appear likely to improve the behavior of these method s.