Fig. 3

a, b Forest plots of Rs (a) and SMD (b) for spontaneous AR assay. Spontaneous AR% were weakly correlated with FR (pooled Rs = 0.32). However, the higher spontaneous AR% was not obtained for higher as compared to lower FRs when pooling SMD (pooled SMD = − 0.30). c–f Forest plots of Rs (c), SMD (d), SEN and SPE (e), DS and DOR (f) for induced AR assay. Induced AR% were positively correlated with FR (pooled Rs = 0.40). Higher induced AR% was obtained for higher as compared to lower FRs (pooled SMD = 0.86). Lower induced AR% was predictive of lower FR with moderate SEN, SPE (pooled SEN = 0.79; SPE = 0.87), and discriminant effect (pooled DS = 3.22; DOR = 24.91). AR acrosome reaction, Rs spearman correlation coefficient, SMD standardized mean difference, SEN sensitivity, SPE specificity, DS diagnostic score, DOR diagnostic odds ratio