Managing the exponential growth of mendelian randomization studies

Much of the research we publish relates to questions of cause and effect. In an ideal world, we would subject these questions to experimentation, randomising study participants to different conditions. However, in many cases – particularly in the context of addiction – such randomization is simply not possible. We cannot randomise tobacco-naïve children to use e-cigarettes, for example, to determine whether or not vaping acts as a ‘gateway’ to subsequent smoking. In these cases, we have to rely on observational methods, and these suffer from well described problems of confounding, including reverse causality.