EBIR

Question 1

What are the benefits of a case control study?

Answer 1

(1) Easier to study rare diseases
(2) Can examine a variety of exposures for a given disease
(3) Compared to cohort studies: quicker, easier, cheaper
(4) Under certain conditions, case control studies can estimate a causal parameter

Question 2

What are the weaknesses of a case control study?

Answer 2

(1) Difficulty in selecting appropriate controls
(2) Information bias (particularly recall bias)
(3) Not ideal for rare exposures
(4) Can be difficult to establish temporality between exposure and disease

Question 3

What is important in selecting controls for case control studies?

Answer 3

• Select individuals who might have become cases in your study IF they had developed disease, that is, rom the source cohort that gave rise to the cases
• Can find controls at a medical center, in the community, or retrospectively look at deceased individuals

Question 4

What is “matching”?

Answer 4

• Individual or group matching
• Pairs individuals with a disease (cases) with individuals or a group without the disease (control) -Makes sure that controls and cases are similar on certain characteristics

Question 5

What is individual matching?

Answer 5

A particular type of control group

• Also called “match pairs”
• Matching occurs subject by subject
• For each case, select one or more controls with characteristics that match that case

Question 6

What is group matching?

Answer 6

A particular type of control group

• Also called “frequency matching”
• For a stratum of cases, select a stratum of controls. The proportion of a characteristic should be the same between cases and controls.
• Often requires that all cases are selected first

Question 7

What is selection bias?

Answer 7

• Control-selection bias (if exposure in selected controls differs from exposure in source cohort)
• Case-selection bias (if exposure in selected cases differs from exposure in source cohort)
• When choosing cases/controls, you want well-defined inclusion/exclusion criteria and sound selection methods

Question 8

What is recall bias?

Answer 8

A type of information bias

• Some patients may not be able to remember or accurately report information related to exposure, or they may not have the required information
• Can be difficult for individuals to remember exposure (unless exposure is something measurable, like the presence/absence of a gene)

Question 9

What is interviewer bias?

Answer 9

A type of information bias

-If interviewers not blinded to cases/controls, they may phrase items differently or probe further on exposure questions with interviewing cases

Question 10

What is confounding bias?

Answer 10

A situation in which the effect or association between an exposure and outcome is distorted by the presence of another variable

• If confounding is present in the source cohort, then it should also be present in the study sample (since cases and controls are selected to be representative of the source cohort)
• Can control for confounding through stratification or statistical modeling

Question 11

What is a case control study?

Answer 11

-Subjects are selected based on DISEASE status –Past exposure status is determined for cases and controls

Question 12

What is the source cohort for case control studies?

Answer 12

The population (cohort) that gave rise to the cases.

Example:
Cases: caffeine addicts at OSUCOM
Source Cohort: OSUCOM

Question 13

Where can you find cases for case control studies?

Answer 13

• Clinic based cases (hospitals, clinics)

- Population based cases (disease registries, death certificates)

Question 14

Which is preferred: incident or prevalent cases?

Answer 14

Incident cases