5. Meta‐regression analyses.

	All trials (n = 158)			All trials excluding German acupuncture trials (n = 154)
Model	Co‐variates [1]	Coefficient (SE) [2]	P value	Co‐variates	Coefficient (SE)	P value
Multiple meta‐regression of all co‐variates simultaneously	Pt‐involved outcome Study aim was placebo	‐0.17 (0.084) ‐0.15 (0.072)	0.047 0.043	Study aim was placebo	‐0.18 (0.072)	0.012
Multiple meta‐regression by stepwise elimination	Pt‐involved outcome Physical placebos  Placebo undisclosed  Study aim was placebo	‐0.18 (0.077) ‐0.13 (0.056) ‐0.17 (0.070) ‐0.14 (0.070)	0.023 0.020 0.014    0.046	Pt‐involved outcome Study aim was placebo Precision	‐0.19 (0.072) ‐0.18 (0.067) 0.025 (0.010)	0.011 0.008 0.016

[1]. We studied 11 predefined co‐variates. A model based on stepwise elimination of the co‐variate with the highest P‐value resulted in four co‐variates with P < 0.05. The model had a tau² = 0.0207, compared to the overall random effects meta‐analysis of tau² = 0.0450. Thus, the model explains 54% of the initial variation. The model was sensitive to the exclusion of the four German acupuncture trials. The inclusion of these trials especially influenced the statistical significance of the importance of disclosing to patients that the trial involved a possible placebo treatment.

[2]. SE: Standard error