Hip fracture or not? The reversed prevalence effect among non-experts' diagnosis

Despite numerous investigations of the prevalence effect on medical image perception, little research has been done to examine the effect of expertise, and its possible interaction with prevalence. In this study, medical practitioners were instructed to detect the presence of hip fracture in 50 X-ray images with either high prevalence (N-signal = 40) or low prevalence (N-signal = 10). Results showed that compared to novices (e.g., pediatricians, dentists, neurologists), the manipulation of prevalence shifted participant's criteria in a different direction for experts who perform hip fracture diagnosis on a daily basis. That is, when prevalence rate is low (p(fracture-present) = 0.2), experts held more conservative criteria in answering fracture-present, whereas novices were more likely to believe there was fracture. Importantly, participants' detection discriminability did not vary by the prevalence condition. In addition, all participants were more conservative with fracture-present responses when task difficulty increased. We suspect the apparent opposite criteria shift between experts and novices may have come from medical training that made novices to believe that a miss would result in larger cost compared to false positive, or because they failed to update their prior belief about the signal prevalence in the task, both would suggest that novices and experts may have different beliefs in placing the optimal strategy in the hip fracture diagnosis. Our work can contribute to medical education training as well as other applied clinical diagnosis that aims to mitigate the prevalence effect.

Automated summary

Despite the prevalence effect being investigated in medical image perception, little attention has been given to examine the influence of expertise and its interaction with prevalence. This study found that experts, who are experienced in diagnosing hip fractures, exhibited a different shift in criteria compared to novices when faced with different prevalence levels. The results suggest that expertise plays a role in shaping diagnostic criteria, and further understanding this phenomenon can contribute to medical education and clinical diagnosis improvement.