Methodological challenges in designing dementia prevention trials - the European Dementia Prevention Initiative (EDPI).

Recent epidemiological studies have indicated numerous associations between vascular and lifestyle related risk factors and incident dementia. However, evidence from randomised controlled trials (RCT) showing effectiveness of interventions aimed at these risk factors in preventing or postponing dementia onset is still lacking. Three large RCTs on multi-component interventions to prevent dementia (preDIVA, FINGER, MAPT) have been initiated in Europe to address these issues. Irrespective of some methodological differences, all three studies target cardiovascular and lifestyle related risk factors. Collaboration within the newly founded 'European Dementia Prevention Initiative' (EDPI) will allow for a comprehensive exploration of optimal target population, intervention and outcome measures, which are currently unknown. Combining data of the ongoing studies and running simulation analyses will facilitate determining the optimal design including accurate sample-size calculations for future multi-national clinical trials on dementia prevention. Interventions aiming at dementia prevention should be pragmatic and easy to implement on a large scale in different health care systems, without generating high additional costs or burden on participants or physicians. As the optimal age for intervention precedes the optimal age for outcome assessment, traditional trial designs might lead to suboptimal timing of either of the two. Separation of intervention and outcome assessment in time is a potential solution, but requires studies with very long follow-up. International collaboration of research groups with experience in dementia prevention studies and well-organised logistics for these major projects is pivotal to success for future large-scale dementia prevention studies. Founding of EDPI is an important first step in this direction.