The SMD estimates of dietary ginger supplementation on growth performance

The SMD estimates of dietary ginger supplementation on growth performance, internal organ weight, total serum lipid level and semen quality and 95% confidence interval (CI) were pooled using the methods of Cohen (1988) for the fixed effects model and DerSimonian and Laird (1986) for the random effects models. In a situation where the study reported separate estimates of measure of SE for production response for each group, they were converted into SD. If the study (ies) reported a common SE or SD, the estimate was used for both control and treatment groups. Also, if a study had two or more ginger intake levels, an overall estimate was calculated to include the study in the treatment groups versus control comparison (Higgins and Green 2011).
The effects of dietary ginger supplementation on sperm production, broiler performance, serum lipid concentration and internal organ weight characteristics were displayed in forest plots, using the estimated SMD of ginger via a random effects model (DerSimonian and Laird, 1986; IntHout et al., 2014). Points to the left of the line of no effect (vertical line) represent a reduction in the outcome of our interest, while the points to the right indicate an increase in the outcome. Each square in the forest plot stands as the mean effect size (ES) for that particular study, while the line connected to the square connotes the upper and lower 95% confidence interval (CI) for the ES. The weight of each study was estimated using inverse of the variance of the ES using the method of Lean et al. (2009). The size of the square box is proportional to the inverse variance of the estimates with larger square boxes representing greater weight.