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Table 16.4.a presents some results that might be available from a report of a cross-over trial, and presents the notation we will use in the subsequent sections. We review straightforward methods for approximating appropriate analyses of cross-over trials to obtain mean differences or standardized mean differences for use in meta-analysis. Review authors should consider whether imputing missing data is preferable to excluding cross-over trials completely from a meta-analysis. The trade-off will depend on the confidence that can be placed on the imputed numbers, and in the robustness of the meta-analysis result to a range of plausible imputed results.