Groups were as different as chalk and cheese

EDITOR—Wei et al say that the results of their observational study of treatment with statins in routine clinical practice in Tayside are consistent with, and similar to, those reported in clinical trials.1 This conclusion is hardly justified.

A cohort of patients, defined by a discharge diagnosis of myocardial infarction between January 1993 and December 2001, was studied to compare the outcomes in those treated with statins and those not receiving these drugs. The data clearly show that the two groups differed substantially in terms of age, sex, comorbidity, and other cardiovascular drug treatment—all of these factors were biased in favour of a poorer outcome in patients not given statins.

Furthermore, the two groups belonged to different time periods, most of the untreated patients to the earlier part and most of those given statins to the later part of the study. Given the changes between 1993 and 2001—including, for example, those related to the management of acute myocardial infarction and the criteria for diagnosis—it is only to be expected that the untreated group would have a higher risk of subsequent cardiovascular events.

Multivariate analysis was reported as showing that statins reduced all cause mortality by 31% and the composite end point of myocardial infarction plus cardiovascular mortality by 18%. These results should be greeted with scepticism.

Firstly, many trials of statins have failed to show any reduction whatsoever in all cause mortality.2^–5

Secondly, as observed in other studies, any reduction in all cause mortality would be expected to be much less than that for composite cardiovascular end points.2 4 5

The two groups in this study were as different as chalk and cheese. It should come as no surprise, therefore, that the results were anomalous. In such circumstances, no amount of statistical trickery could be expected to furnish anything of value.