The goal of the data collection and analyses described in this paper was to investigate the effects of incorrect output from a CAD tool on the reliability of the decisions of its human users. Our work follows on a clinical trial that evaluated the impact of introducing a computerised prompting tool (R2 ImageChecker) as part of the breast screening programme in the UK. Our goal was to use data obtained in this trial to feed into probabilistic models (similar to those used in “reliability engineering”) which would allow us to find and assess possible ways of improving the interaction between the automated tool and its human user. A crucial requirement for this modelling approach is estimating the probability that a human will fail in his/her task when the output of the automated tool is incorrect. The data obtained from the clinical trial was not sufficient to inform this aspect of our probabilistic model. Therefore, we conducted a follow-up study to elucidate further the effects of...