which most of the doctors certifying the deaths will
have been unaware of the contraceptive history of the
deceased woman.
We were able to adjust for the potentially important
confounding factors of age, smoking, social class, parity,
and (for some analyses of the general practice
observation subset) use of hormone replacement therapy.
The adjustments tended to make little difference
to the rates. Smoking data have not been routinely
updated during the study. Use of smoking information
collected at study entry will tend to underestimate the
effects of smoking. This is because women in the
cohort are more likely to have stopped smoking than