Contemporary methodological issues in drug development: the functionality of blinding is poorly studied.

Blinding is an important methodological principle in drug development. This article reviews the functionality of blinding within the context of bias minimizing structures of randomized clinical trials. Blinding is not well understood and not well studied. The risk of bias domain 'blinding' is commonly assumed to be 'low-risk' whenever readers come across randomized clinical trials labeled as 'blinded'. However, empirical evidence has shown that this assumption cannot be taken for granted. The functionality of blinding techniques in preventing bias requires further studies.