A large-scale randomized, double-blinded clinical trial was conducted to evaluate the effect of beta-blocker therapy on the survival of patients with chronic heart failure, class IV. The patients with severe heart failure were randomly assigned to receive either carvedilol (a beta blocker) or a placebo. In their report of the results of the study, the investigators included a table with baseline characteristics (eg, age, race, prevalence of hypertension) of the patients in the treatment and placebo groups. According to that table, both groups had a similar distribution of these characteristics. With the information given, which of the following is most probable?

Question

A large-scale randomized, double-blinded clinical trial was conducted to evaluate the effect of beta-blocker therapy on the survival of patients with chronic heart failure, class IV.  The patients with severe heart failure were randomly assigned to receive either carvedilol (a beta blocker) or a placebo.  In their report of the results of the study, the investigators included a table with baseline characteristics (eg, age, race, prevalence of hypertension) of the patients in the treatment and placebo groups.  According to that table, both groups had a similar distribution of these characteristics.  With the information given, which of the following is most probable?

Quizplus · Accepted Answer

The purpose of randomization is to make the distribution of all potential confounders even (eg, between the treatment and placebo groups). Unlike all the other methods of controlling confounding (eg, matching, stratified analysis), randomization potentially controls known as well as unknown confounders. One of the methods to assess the adequacy of randomization is to look at the distribution of baseline characteristics in both groups. If they are similar, one can assume that the randomization evenly distributed the confounders between the groups, and that randomization was successful. (Choices A and C) From the information given, it is not possible to judge the adequacy of the sample size to detect the difference in the survival (if it is present) between the treatment and placebo groups. It is also not possible to assess the power of the study (which depends on the sample size) based on the above information. (Choice B) The results of the study were not mentioned. (Choice E) Observer bias can be controlled with blinding, not randomization. Educational objective: In clinical trials, randomization is said to be successful when a similarity of baseline characteristics of the patients in the treatment and placebo groups is seen.

A Large-Scale Randomized, Double-Blinded Clinical Trial Was Conducted to Evaluate