Dear Statalist
I�m conducting a meta-analysis for population-based studies of a
rare mortality outcome (stillbirths) using the �metan� procedure.
My question concerns the derivation and interpretation of the study
weights in the final column of this Stata output:
. metan ideath inodeath cdeath cnodeath, rr
label(namevar=studyno)
Study | RR [95% Conf. Interval] % Weight
--------------+-----------------------------------------
1 | 3.5 1.04399 11.7339 6.34589
2 | 4 .4517 35.4217 2.37971
3 | 1.62944 1.02163 2.59886 51.6439
4 | 2.50294 1.25479 4.99266 15.2031
5 | 3.95477 1.15619 13.5274 4.80286
6 | .810097 .282934 2.31947 19.6245
--------------------------------------------------------
MH pooled RR | 1.88825 1.36146 2.61886
--------------------------------------------------------
Heterogeneity chi-squared = 6.35 (d.f. = 5) p=0.273
Test of RR=1 : z= 3.81 p = 0.000
The raw data for studies 4 and 6 are as follows:
Study 4:
(RR=2.50; study weight: 15.2%)
Exposed cohort: deaths (n=8); survivors (n=927)
Unexposed cohort: deaths (n=5,319); survivors (n=1,550,656)
Study 6:
(RR=0.81; study weight: 19.6%)
Exposed cohort: deaths (n=4); survivors (n=614)
Unexposed cohort: deaths (n=25); survivors (n=3,104)
The sample sizes and numbers of events are smaller in Study 6
than in Study 4 and yet Study 6 has the larger study weighting.
Could anyone kindly provide an explanation for this? Thanks.
Regards
Roger Webb
University of Manchester, UK
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