It is important to provide detailed instructions to all authors who will use the data collection form (Stock 1994). These might be inserted adjacent or near to the data field on the form, directly in the cell that contains the data (e.g. as a comment in Microsoft Excel) or, if they are lengthy, might be provided on a separate page. Use of coding schemes is efficient and facilitates a systematic presentation of study characteristics in the review. Accurate coding is important, and the coding should not be so complicated that the data collector is easily confused or likely to make poor classifications. Checks should be made that coding schemes are being used consistently by different review authors.