When working with twins discordant for disease, a matched case–control study can be applied.

Twins are matched for:

• Age
• Genetic factors (perfectly for MZ pairs; 50% for DZ)
• Non-genetic familial factors (not necessarily to the same degree for MZ and DZ pairs)
• Mother, father, uterus and, perhaps, placenta
• Sex, if same-sex pairs
• Calendar year of birth
• Measured factors for which they are the same or similar

Analytic methods

• Binary outcome
• Conditional logistic regression models
• These methods adjust for measured factors

Strengths

• Matched for both measured and unmeasured factors
• Otherwise very similar to standard case–control studies
• Less costly and time-consuming than cohort studies

Limitations

• Potential recall bias
• Inefficient for rare exposures

References

Cockburn, M., Black, W., McKelvey, W. and Mack, T. (2001). Determinants Of Melanoma In A Case-Control Study Of Twins (United States). Cancer causes & control, 12(7), 615-25.

Hamilton, A. S., & Mack, T.M. (2003). Puberty and genetic susceptibility to breast cancer in a case-control study in twins. The New England Journal of Medicine, 348(23), 2313-22.

Oliveira, V. C., Ferreira, M. L., Refshauge, K.M., Maher, C.G., Griffin, A.R., Hopper, J. L. and Ferreira, P. H. (2015). Risk factors for low back pain: insights from a novel case-control twin study. The Spine Journal, 15(1), 50-7.