CONTROL OF BIAS IN DIETARY TRIAL TO PREVENT CORONARY RECURRENCES - THE LYON DIET HEART-STUDY

Background and Objectives: A major limitation of dietary trials is tha t double blind design is not feasible. These trials are therefore pron e to biases. The Lyon diet heart study is a single-blind secondary pre vention trial to test the hypothesis that a Mediterranean-type of diet may prevent recurrences after a first myocardial infarction. A. surpr ising 73% reduction of the risk of new major cardiac events was observ ed in the experimental group. For this reason, it is important to desc ribe the methods used in the trial. We now report our techniques to ra ndomize the patients, to change their diet and to control for possible bias, in particular any investigator or attending physician bias. Des ign: In this dietary trial, a specific design was used to recruit and randomize the patients without informing them and their physicians tha t they were participating in a comparative trial. The attending physic ian bias was evaluated by studying drug usage and the investigator bia s by constructing a questionnaire from which specific scores were used to evaluate (1) how the patients appreciated their participation in t he study and (2) whether this participation resulted in significant ch anges in their way of living. Subjects: 605 survivors of a first myoca rdial infarction were randomized into either a control or a Mediterran ean group. Results: The two randomized groups were similar for all the variables of prognosis. Drug usage was not significantly different be tween groups, suggesting that there was no major attending physician b ias. Analyses of the appreciation scores and of the change score did n ot detect any significant investigator bias. Conclusions: Although the study cannot be completely shielded from minor biases, the data prese nted here provide evidence that the dietary modifications per se were protective, not other (including psychosocial) changes resulting from the participation to the trial.