Randomisation doesn't guarantee similarity of groups; minimisation does

When we have to decide which of two drugs, interventions, or management strategies is the better, the most secure evidence is generally obtained from a randomised controlled trial. The primary objective of randomisation is to ensure that all other factors that might influence the outcome will be equally represented in the two groups, leaving the treatment under test as the only dissimilarity. Any difference in outcome can then be attributed to the treatment effect. But how realistic is this assumption in practice?

When published a randomised trial typically includes a table listing all the prior factors known actually or possibly to influence outcome. The average age and its distribution in each group and the proportion of men and women usually head the list, followed by other likely determinants of outcome. In the case of heart disease these will probably include details of left ventricular function; the proportions in each group with diabetes, hypertension, hyperlipidaemia, or a smoking history; the relative incidence of arrhythmia, obesity, symptoms of heart failure; and any others factors that may have been collected. If these are similar in the two groups (which is …