Placebo response to intra-articular injections in knee osteoarthritis: magnitude, evolution over time, and influencing factors. A systematic review and meta-analysis with meta-regression.

The estimate suggests that each one-point increase in the male-to-female ratio is associated with a 1.4-point decrease in the placebo response (estimate: −1.378, P = 0.04); a tendency towards significance as a potential influencing factor for placebo responses was found for the year of publication, with placebo responses increasing for the most modern studies (estimate: 0.3105, P = 0.07).

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