Bias in treatment trials: avoiding common pitfalls

Rigorous treatment trial exhibit a number of key features to guard against bias. Randomization, blinding (of patients, care staff and assessors), full follow-up on all patients, and 'intention-to-treat' analyses all contribute to removing bias so that any true treatment effect can be revealed. This article outlines the rationale behind these features and advises how bias in treatment trials can be assessed.