As the assessment was undertaken by two assessors, one assessor was with expertise in clinical epidemiology and clinical research methods, and the other was a novice user to these quality assessment instruments, thus it could possibly result in underestimation of the reliability of AMSTAR. Another limitation in this study is lack of backward translation for the adapted tools, the translation into Chinese may produce a different measurement instrument with different properties. The current Chinese version should be translated back into English by a third party, and the back translations would be compared with the original tools to ensure the conceptual equivalence. However, the absence of back translation may offset somewhat in present study by a check of accuracy with a previous Chinese version of two instruments tools [10] .