Multiplicative and additive models with external controls in a cohort study of cancer mortality.

The use of additive and multiplicative hazard models is examined for a cohort study of 2696 women followed up for 12 years. The multiplicative model implied that women with a haemoglobin level less than 12 g/dl were at higher risk from cancer, and the additive model showed that this risk was confined to women after the menopause. Despite difficulties in fitting and in interpretation, additive model can be useful in the analysis of cohort studies.