Meta-analytic methods for pooling rates when follow-up duration varies: a case study

Table 4 Summary Outcome Measures for Emergency Room Visits.

Measure	Effect Size	Confidence Interval	Effect Size P-value	Homogeneity Test P-value
SMD^a
Fixed-effects	-0.21	-0.33, -0.09	<0.001	0.05
Random-effects	-0.27	-0.45, -0.09	0.003	0.05
IRD^b
Fixed-effects M-H	-0.04	-0.05, -0.03	<0.001	<0.001
Random-effects	-0.05	-0.08, -0.03	<0.001	<0.001
IRR^c
Fixed-effects M-H	0.66	0.59, 0.74	<0.001	<0.001
PR + study indicators	0.66	0.54, 0.81	<0.001	<0.001
PR – study indicators	0.77	0.59, 0.99	0.039	N/A

^a SMD refers to standardized mean difference and was obtained using both fixed effects and random effects models. ^b IRD refers to the incidence rate difference, and was obtained using a Mantel-Haenszel procedure to estimate a fixed-effects model and an inverse-variance method to estimate a random-effects model. ^c IRR refers to the incidence rate ratio and was obtained using Mantel-Haenszel procedure to estimate a fixed effects model and Poisson regression models with Huber-White sandwich estimators with and without study indicators which is equivalent to a random-effects model.

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