STUDENT CASE STUDY, PART TWO B: CASE CONTROL STUDY― SINGER-FREEMAN
MMR VACCINE AND AUTISM: SCIENTIFIC INQUIRY, ETHICS, AND EVIDENCEBASED PROBLEM SOLVING
CASE STUDY FOR THE AACU STIRS PROGRAM
Karen Singer-Freeman, Associate Professor of Psychology, Purchase College, State University
of New York
STUDENT CASE
Part Two B: Case Control Study
How Can We Study the Effects of Potentially Dangerous Treatments? Methods Used in the Study
of Vaccines and Autism
Case Control Study
In a case control study we identify individuals with a disease (cases) and find other individuals
(controls) who do not have this disease but are otherwise similar to those with the disease in as
many ways as possible. To increase the statistical power (the probability that a statistical test
will correctly reject the null hypothesis when the null hypothesis is false) of the research design,
each case is often matched with multiple controls, particularly if the number of cases is limited.
Matching controls to cases on age, sex, or other known disease risk factors increases the
likelihood that the controls as a group will be similar to the case in important ways.
Once the cases and controls have been selected, the researcher looks back in time using
surveys, medical records, or other forms of previously collected data to determine whether the
cases or the controls in the study received the treatment of interest, in this case the MMR
vaccine (the hypothesized trigger for autism). Researchers determine whether cases are more
likely to have experienced a potential trigger for their disease than controls. If exposure to the
hypothesized trigger is higher among cases than controls, it suggests that there might be an
association between the trigger and control.
However, a case control study will not allow us to conclude that the MMR vaccine causes
autism because the cases and controls we select may differ in other important ways. Because
we did not randomly assign subjects to groups, there may be other differences between the
groups that cause the differences we believe to be resulting from our exposure (in this case, the
MMR vaccination). Accordingly, even when an association is seen between a trigger and a
disease the researcher cannot conclude that the trigger causes the disease. Figure 7
summarizes the key features of case control design.
STUDENT CASE STUDY, PART TWO B: CASE CONTROL STUDY― SINGER-FREEMAN
Children with Autism are
identified
Each child with Autism is
matched with a similar child
who does not have Autism
History of MMR
vaccination is
collected from
medical records for
both groups of
children and
compared
Figure 7. A Case Control Design to Examine the Association between the MMR Vaccine and
Autism.
A Real Case Control Study
Uno, Uchiyama, Kurosawa, Aleksic, and Ozaki (2012) identified 189 individuals with autism
(cases) and 224 controls who were matched by sex and birth year to the cases.
Key Questions
23)
Are there any other risk factors the cases and controls should have been matched for?
Explain your answer.
24)
If the MMR vaccine causes autism, which group should have had a higher rate of
vaccination coverage (meaning a higher percentage of children in this group received
the MMR vaccine)?
Uno et al. 2012 found that vaccination records were not significantly different between the
cases and the controls. The authors concluded that neither receipt of the MMR vaccine nor the
total number of vaccines received were associated with increased risk of autism.
Key Questions
25)
Can you think of a reason we might not see higher vaccination rates among children
with autism even if the MMR vaccine does cause autism in some children? Propose
another factor that could cause children to develop autism.
26)
Would it be useful to record the date of the MMR vaccine and the date of autism
diagnosis for each child in the study? Explain your answer.
27)
Propose another way to study the association between the MMR vaccine and the
development of autism. Be sure to include the group or groups you would study, the
information you would gather, and how this study would add to our understanding of
vaccine safety.
Once your group is done with these questions, please see your instructor for guidance on next
steps.