The Case-Only Odds Ratio as a Causal Parameter
Article first published online: 11 MAR 2004
Volume 60, Issue 1, pages 233–240, March 2004
How to Cite
Rosenbaum, P. R. (2004), The Case-Only Odds Ratio as a Causal Parameter. Biometrics, 60: 233–240. doi: 10.1111/j.0006-341X.2004.00154.x
- Issue published online: 11 MAR 2004
- Article first published online: 11 MAR 2004
- Received December 2002. Revised July 2003. Accepted September 2003.
- Case-only study;
- Causal effect;
- Gene–environment interaction;
- Observational study
Summary. In the simplest case-only design, cases of a disease are cross-classified into a 2 × 2 table describing a genotype attribute and exposure to some environmental agent. In some instances, the genetic attribute has described inherited genes; in other instances, it has described mutations, for instance, damage to proto-oncogenes or tumor suppressor genes leading to cancer. Here, the population case-only odds ratio is written as a causal parameter in terms of potential outcomes with and without exposure to the agent. It is shown that the case-only odds ratio makes sense as a causal parameter with inherited genes, but its magnitude does not have a causal interpretation with mutations, although deviations from 1 do provide information. The difference is that the environmental agent certainly did not cause an individual to inherit particular genes, but it may have caused the mutation.