Fig. 1

Flow diagram of records selection Legend: This figure indicates the flow chart of study selection. The identification step lists the number of records identified in the initial search and the updated search, and the number of duplicate records removed. The screening step lists the number of screened and number of records excluded based on titles and abstracts. The eligibility step lists the number of records for which full text were retrieved to determine eligibility of study and the number of records excluded per reason. And finally, the last step lists the number of records as well as the number of unique studies included in the review. The updated search yielded an additional 11 unique studies included in the review from those of the initial search