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Statistical analysis
A meta-analysis was conducted on the extracted production outcomes using OpenMEE, the open source, multi-platform software for meta-analysis in ecological and evolutionary biology (Wallace et al. 2016). Continuous data were analyzed using standardized mean difference (SMD), normally called effect size. The difference between treatment and control means was standardized using the values of the SD of the control group and treatment group. Effect sizes set the magnitude of an effect of interest (in this case the effect of dietary ginger supplementation on growth performance, organ weight, blood lipids and semen quality) and provide the common statistical parameter that allows the combination and comparison of estimate from different studies into a single and standardized metrics (Rosenberg et al. 2013). In the current study, the authors used Hedges’ d, and the SMD between ginger in control and treatment groups to determine the effect size (Borenstein et al. 2009). The most common and preferred metrics in meta-analysis is Hedges’d (Hedges and Olkin, 1985; Koricheva et al., 2013). One major advantage of Hedges’d over the response ratio metric is that Hedges’d can be used for studies with small sample sizes. In addition, Hedges’d is not influenced by unequal sampling variance in paired groups, in comparison to the response-ratio metric (Gurevitch et al., 1992; Morales and Traveset, 2009). Importantly, Hedges’d is the most preferred metric of effect size in studies that report X and SDs for the purposes of comparing the control and treatment groups in terms of continues response variable (Borenstein et al., 2009). In current study, Hedges’d was computed using the following equation: