Commentary: The hormone replacement-coronary heart disease conundrum: is this the death of observational epidemiology?

Under its definition for the word ‘hindsight’ the Oxford English Dictionary includes the following statement ‘hindsight is always better than foresight’ (http://dictionary.oed.com/), and the slogan of a private survey and evaluation company, ingeniously called Hindsight, is ‘remember hindsight is always 20/20!’ (http://www.hndsight.com/). We have the benefit of the ‘hindsight’ from randomized controlled trials (RCT) when we comment on this meta-analysis of observational studies, but whether the conflicting results between the trial and observational evidence on the association between hormone replacement therapy (HRT) use and coronary heart disease (CHD) will lead to 20/20 vision remains to be seen. The disparity between findings from observational studies and RCT of the effects of HRT on CHD,1–4 has created considerable debate among researchers, practitioners and postmenopausal women. The authors of the meta-analysis reprinted in this issue of the International Journal of Epidemiology concluded that the pooled estimate of effect from . . .