2.3 Quality Assessment and Data Extraction
Two independent investigators (Z.Y. and X.W.) evaluated the quality of all studies according to 11-item checklist that was recommended by the Agency for Healthcare Research and Quality (AHRQ)13subjectively. “0” will be scored if it was answered No or Unclear and “1” will be given to the answer Yes. Quality of articles was assessed as follows: “0–3” means low quality, 4–7 means moderate quality, 8–11 means high quality. The following information was extracted: first author, publication time, study design, source of population, mean age or age range, the sample size and outcomes.