Systematic review of copper intrauterine contraception continuation in young nulliparous women based on intrauterine device type.

Conventionally, while an I 2 value <40% may not be significant, a value >50% may represent substantial heterogeneity and a value >75% may indicate considerable heterogeneity. 15 The tau 2 statistic measure of ‘between-study variance’, unlike the I 2 statistic, is not affected by size of included studies in a meta-analysis and hence may be considered more appropriate for estimating heterogeneity. 16 The effect of removing individual studies on the overall effect size (ES) was explored in sensitivity analyses ( online supplemental material 4 ).

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