SectionB: Calculating Measures ofAssociation

Over 25 studies have been conducted which have failed to show an association between MMR vaccine and autism. Below are some data from two of these studies (one cohort and one case-control). Calculate the measure of association for each study after completing the 2x2 table and interpret the measure of association.

1. Cohort study by Madsen et al (NEJM2002)

Of the 537,303 children in the cohort, 440,655 (82.0 percent) had received the MMR vaccine. We identified 316 children with a diagnosis of autistic disorder; 263 of the cases had been vaccinated with MMR (83%); 53 children with autism had not been vaccinated.

1. Case control study by Smeeth et al (Lancet2004)

1294 cases of pervasive developmental disorder (PDD) and 4469 controls were included. 1010 cases (781%) had MMR vaccination recorded before diagnosis, compared with 3671 controls (821%) before the age at which their matched case was diagnosed.