*Geek Box: HRT

*Geek Box: The Famous HRT Example

Any medical student likely knows this by heart at this stage. In a cohort study published in 1996,  an association was found between post-menopausal women taking hormone-replacement therapy and reduced risk of cardiovascular disease. Following this study, a subsequent randomised controlled trial in fact found that post-menopausal women taking HRT were at increased risk of cardiovascular disease.

Because of the differential status in ‘standard’ of evidence applied to cohort studies vs. RCTs, the discrepancy between the two studies was reconciled in favour of the RCT: the RCT result was deemed to be the “right” result, because it was assumed the observational study result was invalid if the RCT found otherwise. However,  understanding of the relationship between the timing of menopause and cardiovascular disease ultimately indicated that the discrepancy in the results related to the timing of menopause relative to when HRT was initiated. Women with early-onset menopause tend to be at higher risk for CVD. Thus, when both studies were analysed through this lens – age of menopause onset relative to initiation of HRT – both studies were ‘right’: their answers were correct for their respective population subgroups who had been studied.