“…Twenty two studies were of moderate quality [19, 23-25, 28, 29, 32, 33, 35, 36, 39, 41, 43, 45-48, 51, 53, 79, 80]. Two studies only were of poor quality [68,70]. Sixteen studies included failed to clearly describe how participants were selected [19, 24, 28, 29, 33-35, 48, 51, 52, 56, 57, 59, 61, 70], and twenty-two studies used sampling strategies that had the potential to introduce selection bias [19, 22, 23, 25, 29, 32, 34, 37, 39, 43, 45-48, 50-52, 55, 59, 62, 63, 67, 71, 91].…”