This article (1) has been retracted at the request of the authors. The journal received Letters to the Editor from Boyle and Fritschi (2), and from Labrèche and colleagues (3), pointing out a number of misclassifications and methodologic flaws in the meta-analysis. Misclassification of exposure led to the questionable eligibility of articles included in the study and methodologic flaws led to the inclusion of inappropriate studies and the inclusion of articles providing overlapping data. The authors made efforts to correct the errors. After excluding inappropriate and overlapping articles, 47 of the original 61 articles remained and, although some results were similar, conclusions were changed. The authors regret any inconveniences or challenges resulting from the publication and subsequent retraction of this article.
A copy of this retraction notice was sent to the last known e-mail addresses of the authors. Two authors (Xia Yuan and Xuelei Ma) agreed to the retraction; the remaining authors (Chenjing Zhu, Manni Wang, Fei Mo, and Wei Du) did not respond.