6. Single Blind

A trial in which one party, the investigator or, usually, the participants, is unaware of what medicine the participant is receiving. Also called single-masked studies they provide some control when double blinding is impossible or not appropriate.
Single-blind trials are used where the experimenters either must know the full facts (for example, when comparing sham to real surgery) and so the experimenters cannot themselves be blind, or where the experimenters will not introduce further bias and so need not be blind. However, there is a risk that subjects are influenced by interaction with the researchers – known as the experimenter's bias.