Together with HdH and AvHV I wrote an article for the Dutch NTVG on Mendelian Randomisation in the Methodology series, which was published online today. This is not the first time; I wrote in the NTVG before for this up-to-date series (not 1 but 2 papers on crossover design) but I also wrote on Mendelian Randomisation before. In fact that was one of the first ‘ educationals’ I ever wrote. The weird thing is that I never formally applied mendelian randomisation analyses in a paper. I did apply the underlying reasoning in a paper, but no two-stage-least-squares analyses or similar. Does this bother me? Only a bit, but I think this just shows the limited value of formal Mendelian Randomsation studies: you need a lot of power and untestable assumptions which greatly reduces the applicability of this method in practice. however, the underlying reasoning is a good insight in the origin, and effects of confounding (and perhaps even others forms of bias) in epidemiological studies.Thats why I love Mendelian Randomisation; it is just another tool in the epidemiolgists toolbox.