2.6. Analyses and measures of treatment effect:
For each trial, mean differences and standard deviation were calculated for continuous variables. The differences of mean changes in cortisol and testosterone concentration and their correspondence SD were extracted as the effect size. In trials that the standard error (SE) measure was reported, SE was converted to SD applying this formula: SD= SE×√n (n=number of subjects in each group). Between-study heterogeneity was assessed using the chi-squared (χ2) test and quantified applying the I2 statistic, which shows the total variation percentage across studies that is ascribable to heterogeneity rather than to chance. Significant heterogeneity was defined with a P-value of <0.05.
The random effects model was applied to calculate the weighted mean differences (WMDs) with 95% confidence intervals (CIs) for estimating the overall effect. To evaluate whether the outcomes could have been altered by a single study distinctly, a sensitivity analysis was performed (28). Also, subgroup analysis was conducted, based on the sports type (resistance training or aerobic and anaerobic combined training) and duration of studies (over six weeks and 6 weeks or lower). Publication bias was evaluated by Egger’s regression asymmetry test and Begg’s rank correlation test. Funnel plots also depicted the effect sizes against their corresponding standard errors. Statistical analyses were conducted applying STATA 11.2 software (StataCorp, College Station, Texas, USA).