Concepts in epidemiology: the cohort effect

Terence M Mills
Med J Aust 2012; 196 (5): . || doi: 10.5694/mja11.10627
Published online: 19 March 2012

Incidence rates of cancer vary over time;1 this is called a “period effect”. Incidence rates of cancer also tend to increase with age;1 this is called an “age effect”. Another time variable that is associated with the incidence of cancer is year of birth of the patient — the “cohort effect”. Many authors have used real data to emphasise the importance of cohort effects for assessing trends in incidence.2,3 Here, I present a simple, hypothetical example to illustrate the cohort effect.

  • Terence M Mills

  • Loddon Mallee Integrated Cancer Service, Bendigo, VIC.


Competing interests:

No relevant disclosures.


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