In cases the between-study heterogeneity was high, we evaluated the source of heterogeneity using sequential algorithm [23]. According to this algorithm, one study was excluded from the calculations each time. The study that was responsible for the largest decrease in I2 was dropped. This process was repeated for a new set of n-1 studies. We continued by successively reanalyzing reduced sets of studies until I2 dropped below the intended threshold 50%. When there was a chance more than one omitted studies could result in I2 dropping below the desired threshold, we reported the minimum I2.
