“…A significant number of eligible systematic reviews were based on studies other than randomized controlled trials and were thus omitted from the syntheses [14,23,[38][39][40]42,44,47,52,56,58,59,61,63]. Some systematic reviews based only on randomized controlled trials had a high or unclear risk of bias, which further decreased the number of synthesized systematic reviews [13,22,34,35,41,43,45,46,49,53,55,57,60].…”