Evaluating capture-recapture models with two inspectors

Capture-recapture (CR) models have been proposed as an objective method for controlling software inspections. CR models were originally developed to e stimate the size of animal populations. In software, they have been used to estimate the number of defects in an inspected artifact. This estimate can be another source of information for deciding whether the artifact require s a reinspection to ensure that a minimal inspection effectiveness level ha s been attained. Little evaluative research has been performed thus far on the utility of CR models for inspections with two inspectors. In this paper , we report on an extensive Monte Carlo simulation that evaluated capture-r ecapture models suitable for two inspectors assuming a code inspections con text. We evaluate the relative error of the CR estimates as well as the acc uracy of the reinspection decision made using the CR model. Our results ind icate that the most appropriate capture-recapture model for two inspectors is an estimator that allows for inspectors with different capabilities. Thi s model always produces an estimate (i.e., does not fail), has a predictabl e behavior (i.e., works well when its assumptions are met), will have a rel atively high decision accuracy, and will perform better than the default de cision of no reinspections. Furthermore, we identify the conditions under w hich this estimator will perform best.