Fig. 3

Random-effects meta-analysis Forest plot showing standardized mean differences (SMDs) for each study of Zingiberaceae extracts included in the quantitative analysis, sorted by date of publication. The meta-analysis findings indicated that Zingiberaceae extracts significantly reduced subjective pain (P = 0.004; SMD -0.67; 95 % CI -1.13 to -0.21). Earlier studies tended to use lower doses, which may explain the tendency for more recent studies to have larger effect sizes. Each study is represented by a square, with the area of the square corresponding to the weight given to that study in the meta analysis (weighting based on the number of subjects in each trial). The estimated overall effect size is displayed as a diamond. Horizontal lines show 95 % confidence intervals