Past exam of the mathematics course of the University of Cambridge / 2010 / iii / Paper 34 / 1 / h / Solution

The displayed information does not establish increased maternal mortality caused by elective exposure. There are no observed deaths in that group, and the reported adjusted estimate concerns a composite adverse outcome, not death alone. A composite can show an association driven by nonfatal components without identifying a mortality effect.

If the logistic regression and its adjustment are correct, its confidence interval supports an adjusted association with the composite outcome. Calling that association a causal increase in risk additionally requires a defensible comparison group, adequate control of confounding, valid outcome classification and a well-defined intervention. The crude result is in the opposite direction, and the implied very low counterfactual baseline risk deserves examination. Conversely, zero deaths does not prove absence of harm. The justified conclusion is an association conditional on model and study assumptions, with mortality and morbidity distinguished.