The diagnostic pitfalls of surveys: if you score positive on a test of addiction, you still have a good chance not to be addicted. A response to Billieux et al. 2015
Background and aims: Survey-based studies often fail to take into account the predictive value of a test, in other words the probability of a person having (or not having) the disease when scoring positive (or negative) on the given screening test. Methods: We re-visited the theory and basic calculations of diagnostic accuracy. Results: In generally, the lower the prevalence the worse the predictive value is. When the disorder is relatively rare, a positive test finding is typically not useful in confirming its presence given the high proportion of false positive cases. For example, using the Compulsive Buying Scale (Faber & O'Guinn, 1992) three in four people classified as having compulsive buying disorder will in fact not have the disorder. Conclusions: Screening tests are limited to serve as an early detection “gate” and only clinical (interview-based) studies are suitable to claim that a certain behaviour is truly “pathological”
