where E is the expected number for m3, based on the published relative risk (RR), that is:

The approximate variance of the observed minus expected numbers of people with lung cancer who are exposed to environmental tobacco smoke is:

The variance of the natural logarithm of the relative risk was calculated using the published confidence limits for the estimate of the relative risk, except for one study (Gillis et al., 1984), where the method given above for the case-control studies use used since no confidence limits were available.


The overall values for the case-control studies were calculated by adding the values of Observed−Expected (i.e., O−E) and their variance for the individual studies as follows:

and for the variance:

(Yusuf et al., 1985).

For the prospective studies, the overall value for the ln RR was calculated as:

and for the variance:

(Kleinbaum et al., 1982).

The overall value, for all of the studies combined, was obtained

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