2.3. Meta-Analyses

We performed meta-analyses to calculate the differences between control (non-stimulated) and EPS-stimulated cells for the biological indices having enough data for such an analysis. In cases of unreported values, we used WebPlotDigitizer (v4.5, 2021) to extract the information from the given graphs [34]. Meta-regression analysis was used to evaluate the association between duration of stimulation and levels of expression of the examined biological parameters. In cases where the number of replicates was not identified, we assumed that they were conducted in triplicates, and in cases of a range of number of replicates, we used the mean. Since different methods and scales were utilized in the eligible studies, we used standardized mean differences (SMDs) instead of absolute mean differences to standardize our findings to uniform scale [35]. Missing SDs were imputed using the average coefficient of variation from all complete cases [36]. A random effect model was used to account for heterogeneity due to different cell lines, stimulation protocols, and stimulators. All analyses were performed using the “metafor” package in the R language (Rstudio, version 1.3.1093, PBC, Boston, MA, USA). The “atransf” argument in “metafor” was used for the transformed standardized mean difference as an estimate of the log odds ratio. The level of significance was set at an alpha level of p < 0.05.