In this way, the efficacy of tDCS was explored by calculating etc random model effect sizes (Hedges’ g) based on percentage change in tinnitus intensity in active and sham groups. Random-effects model is considered more conservative than a fixed-effect model, since it takes into account the variability between studies, thus leading to wider confidence intervals (CIs) [35]. The meta-analysis was undertaken using Comprehensive Meta-Analysis (CMA) Version 2 software (Biostat, Englewood, New Jersey, USA).3. Results3.1. Included StudiesAn initial search using keywords ��transcranial direct current stimulation�� or ��tDCS�� screened a total of 714 articles. Adding another keyword ��tinnitus�� sorted out 17 articles from 714. Of 17, six studies that met the above-mentioned inclusion criteria were included in the systematic review and are summarized in Table 1.

Of the included studies, 3 were open-label trials and 3 were RCTs. The meta-analysis included 2 of 3 RCT studies and a total of 27 patients with tinnitus were randomized to active tDCS and 27 were randomized to sham tDCS. A flow diagram of the initial identification and attrition to the final selection of the studies is demonstrated in Figure 1.Figure 1Illustration of the steps of study selection.Table 1Summary of the 6 studies that were included in the current study.3.2. Weighted Mean Percentage Responders to Active tDCSThe data of mean percentage responders to active tDCS were available in 2 RCT studies [30, 37] and 3 open label studies [38�C40]. The weighted mean for percentage reduction of tinnitus intensity with active tDCS was 39.

5% (RCT 17.6%, open label 11.6%), ranging from 29.9% [38] to 46.7% [39].3.3. Weighted Mean Percentage Reduction of Tinnitus Intensity by tDCSThe data of mean percentage of tinnitus intensity reduction were available in 3 RCT studies [30, 36, 37] and 2 open label studies [38, 39]. The weighted mean for percentage reduction of tinnitus intensity with active tDCS was 13.5% (RCT 17.6%, open label 11.6%), ranging from 8.0% [38] to 30.4% [30].3.4. A Comparison between Left Temporal Area (LTA) tDCS and Bifrontal tDCS with regard to Weighted Mean Percentage RespondersThe data of mean percentage responders to active tDCS were available Cilengitide in 2 LTA tDCS studies (all RCTs) [30, 37] and 3 bifrontal tDCS studies (all open-label trials) [38�C40]. The weighted mean percentage of responders to active LTA tDCS were 37.0% (range, 35%�C42.9%), while that to active bifrontal tDCS was 40.2% (range, 29.9%�C46.7%).3.5.