title: Positive bias of the combined effect of risk factors estimated by marginal aetiological fractions.
abstract: The method of aetiological fractions is a commonly used epidemiological technique which attributes a certain fraction of each event of interest to a risk factor. An unrecognized property of this method is that when marginal analyses are done, the combined fraction attributed to the risk factors can be considerably overstated, particularly for prevalent risk factors such as alcohol and tobacco. In this paper a practical example of this problem is given. Theoretical bounds on the bias are derived and evaluated for a range of relative risks that are typical for alcohol and tobacco. It is shown that the overstatement can be quite substantial.
authors.affiliation: Department of Statistics, Faculty of Economics and Commerce, Australian National University, Canberra.
authors.forename: T J
authors.initials: TJ
authors.lastname: O'Neill
mesh_terms: D000428:Alcohol Drinking / Q000009:adverse effects / Q000453:epidemiology; D001315:Australia / Q000453:epidemiology; D015982:Bias; D004812:Epidemiologic Methods; D006801:Humans; D008297:Male; D015995:Prevalence; D012307:Risk Factors; D012907:Smoking / Q000009:adverse effects / Q000453:epidemiology