“…Studies that explicitly stated limitations or confounders were just over two-thirds of the total (Table 2),. 13,14,19–22,24,28–56,71,74,76,77,80–95,108,109,115–132,140–145,147–165,169–180,182–184,188–191,193–198 The most commonly mentioned limitation was small sample size, 20,22,24,28,29,32,33,35,37,39,40,42,45,47,52,54-57,74,80,82,86,87,89,93,95,109,118,119,121,123,126,129,141,143,145,148,149,154-159,161,164,169,172,183,198 followed by generalizability issues, 14,19-21,34,38,41,42,44,52-56,80,81,87,89,109,127-130,142,148,151,155,156,162,171,175-177,184,188,189,191,193,196 recall bias, 14,148,150,157,171,173,182,184 heterogeneous groups, 29,42,54,89,142,174,176,177 homogenous groups, 21,38,39,44,45,91,164 and convenience samples. 14,161,176,177,196…”