Although in Merrill Singer's conceptual work on syndemics the study of disease interaction is a central issue, most empirically based research studies have not used appropriate statistical models to do so. This problem was highlighted in a 2015 review. The majority (78%) used a statistical model, which provided no information about disease interaction. The methodological and public health consequences of this type of statistical model were further highlighted. While this criticism does not undermine the concept of disease concentration, it highlights a seriously flawed way of syndemics investigations.