Date	Event	Description
11 November 2009	New search has been performed	The update (published on issue 1 2010) includes 234 trials (52 trials added) and over 16,000 patients. The updated review includes more precise subgroup analysis, especially among trials with low risk of bias, and involves meta‐regression analyses to explain heterogeneity.
11 November 2009	New citation required and conclusions have changed	We have applied new methods and use Summary of Findings tables to assist in conveying the main findings. In contrast to the previous versions of the review (Hróbjartsson 2004a) we now find both a notable pooled effect of placebo in trials with low risk of bias, especially on pain, and a large variation in effects among trials with low risk of bias. Also new is the identification of five factors explaining roughly half of the variation. However, when all trials are pooled, disregarding the risk of bias, results are fairly similar to the previous versions.