Editor—Wei et al reported that statins are as effective in the community as in clinical trials in the secondary prevention of coronary heart disease, but they have not commented on some even more surprising results.1 They reported benefit for calcium blockers, in contradiction of previous findings2-4 and found β blockers to be much more effective than previously thought (odds ratio for risk reduction 0.38 v 0.81 in a previous systematic review2).
We are concerned that these unusually positive findings across the board may reflect an undetected bias in the study design, rather than the true benefit of drug treatment. The marked differences between the intervention and control groups have already been pointed out by Penston [first letter], and most of these differences were controlled for in the analysis. However, the significant rise in statin use from 3% in 1993 to 63% in 2001 means that the intervention and control groups are effectively cohorts from different time periods. This would also affect the results for β blockers and calcium blockers, both of which were much more commonly used in the statin group.
It is not possible to draw meaningful conclusions from this study until the effect of date of discharge from hospital is allowed for in the analysis, and we therefore suggest that the authors reanalyse the data to take this into account.
Competing interests: None declared.
References
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