Mediterranean Diet and Risk of Heart Failure: Results from the PREDIMED Randomized Controlled Trial. Eur J Heart Fail 2017; 19 :1179–1185. doi: 10.1002/ejhf.750

Some departures from the individual randomization protocol affecting a small subset of participants in the PREvención con DIeta MEDiterránea (PREDIMED) trial (at most 14%) have recently been reported in the re-publication of the main PREDIMED paper. 1 For this reason, the authors wish to make the following clarifications and corrections to their original PREDIMED sub-study examining the effect of the Mediterranean diets (MedDiets), supplemented with extra-virgin olive oil (EVOO) or nuts, on the risk of heart failure. 2 In the original sub-study, as reported in detail elsewhere, 1 some participants (n = 425, or 5.7% of the total sample) were directly allocated, since they were recruited, to the same arm of the trial as their relatives because a previous member of the same household (usually the spouse) was already randomized in the trial.Also, centre D, one of the 11 recruiting centres (n = 646, or 8.7% of the total sample), had allocated a subset of its participants by clusters (clinics), instead of using individual randomization (35 participants from centre D were also second household members).The authors have re-analysed the effect of the intervention on the incidence of heart failure after adjusting for propensity scores (built with 30 predictors of allocation to each intervention group) and using a robust estimate of the variance to correct for intra-cluster correlation,