The epidemiology of environmental tobacco smoke (ETS) and the weight of evidence argument.

This paper demonstrates that Wald's meta-analysis is an unadjusted combination of unadjusted estimates. There are many differences among the design and implementation of the original studies combined here. One consequence of these differences is that studies of spousal smoking and lung cancer mortality conducted in the United States have a lower combined RR than those done elsewhere. Here it is shown that adjustment for this stratification results is a non significant finding as to the association of ETS with lung cancer. Likewise, the addition, for illustration, of Varela's Ph.D. thesis that is the largest case-control study to date, changes the overall results from a significant to a non-significant result. This paper does not attempt to update Wald's meta-analysis with more recent studies. This is being done, I believe by the Environmental Protection Agency. I have given here my reasons for suspecting the conclusions of meta-analysis of non-randomized studies and the illustrations provided here of the effect of publication bias and covariate adjustment support this view.