The Cognitive Reflection Test (CRT) was devised to measure the inhibition of heuristic responses to favour analytic ones. Toplak, West and Stanovich (2011) demonstrated that the CRT was a powerful predictor of heuristics and biases task performance - proposing it as a metric of the cognitive miserliness central to dual process theories of thinking. This thesis was examined using reasoning response-times, normative responses from two reasoning tasks and working memory capacity (WMC) to predict individual differences in performance on the CRT. These data offered limited support for the view of miserliness as the primary factor in the CRT. The strongest predictor of CRT in both experiments was WMC. It is argued that while cognitive miserliness has been implicated in CRT performance, participants must also possess the requisite WMC and mindware to successfully complete it. Therefore, the psychological and psychometric properties of the CRT require continued study.