Table 3

Meta-regression results

Mediators		Coefficient	2.50%	97.50%	P value
Study year		−0.002	−0.05	0.05	0.94
Mean age		−0.039	−0.08	0.00	0.07
% males		0.004	−0.00	0.01	0.47
Study length in weeks		0.04	−0.03	0.11	0.29
Risk of bias (low is the reference level)	Some concerns	−0.094	−0.55	0.36	0.68
Risk of bias (low is the reference level)	High	0.038	−0.45	0.53	0.87
Stage (curative is the reference level)	Palliative	−0.307	−0.71	0.10	0.14
Number of sites		0.003	−0.01	0.01	0.67
Type of study (parallel arms trial is the reference level)	X-over	−0.009	−0.52	0.51	0.97
Subjects in the placebo arm (categorical variable, 0–50 is the reference level)	51–199	0.117	−0.	0.53	0.58
	200+	0.165	−0.49	0.82	0.62
Subjects in the placebo arm (continuous variable)		0	−0.002	0.003	0.74
Tool item (single is the reference level)	Multidimensional	−0.102	−0.73	0.53	0.75
Placebo dosage regimen (fixed dose is the reference level)	Flexible dose	−0.001	−0.44	0.43	0.99
Type of drug (other is the reference level)	Psychostimulants	0.157	−0.22	0.53	0.41