Classes 20-21 Case-Control Studies

Question 1

Define Case-Control Studies

Answer 1

Observational, analytical studies allowing researcher to be passive observer of natural events occurring in individuals with the disease/condition of interest (cases) who are compared with people who do not have the condition of interest (controls)

Question 2

In Case-control studies, group assignment is based on:

Answer 2

Disease Status

Question 3

When are case-control studies useful?

Answer 3

When studying a rare disease or investigating an outbreak

Question 4

Case-control studies commonly generate the _____ ______ as measure of association

Answer 4

Odds Ratio (OR)

Question 5

Reasons to select a Case-Control design:

Answer 5

Unable to “randomize”
Limited resources
Disease of interest is rare
Prospective exposure date is difficult/expensive to obtain and/or very time inappopriate

Question 6

Case-Control Studies are always:

Answer 6

Retrospective

Question 7

Strengths of Case-Control Studies

Answer 7

Good for assessing multiple exposures of one outcome
Useful when diseases are rare
Useful in calculating odds or OR’s
Less expensive
Useful when ethical issues limit Interventional studies
Useful in dynamic populations
Useful when disease has long induction/latent period

Question 8

What does it mean for a study to be retrospective?

Answer 8

This means that the outcome is already known

Question 9

Selection of cases in Case-control studies

Answer 9

Defined by the investigator using accurate, medically-reliable, and efficient data sources
Should be objective, consistent, and valid

Question 10

Weaknesses of Case-control studies

Answer 10

Opposite of the strengths

Question 11

Selection of controls in Case-control studies

Answer 11

DIFFICULT
Major determinant in whether any conclusion is valid (internal validity)
Make the groups as close as possible except the presence of the disease (control) of interest
Must be selected irrespective of exposure status

Question 12

What is the goal in selecting controls in case-control studies?

Answer 12

To assess for the presence of an association between exposure & known condition of interest be selecting non-disease individuals from the sample population which produced the cases

Question 13

True or False:

In a case-control study, it is possible for an individual to be both a case and a control in the same study

Answer 13

TRUE
Can be associated with an outbreak investigation with multiple exposures OR in a situation of brief (acute) change in risk of the outcome in interest (hazard period) - “case-crossover” design

Question 14

Describe a “case-crossover” design in case-control studies

Answer 14

Subjects are their own controls during the other times they don’t have the acute change in risk
Only Case-Control study design able to adequately attempt to address issue of “temporality”

Question 15

Nested Case-Control Studies

Answer 15

Case-Control Studies conducted after, or out of, a prospective Cohort study
Subjects in cohort study ultimately developing disease are defined as cases
Diseased used in a new (different) study design

Question 16

Sampling types of controls used for nested case-control studies or when sampling is necessary from Cohort:

Answer 16

Survivor Sampling
Base Sampling
Risk-Set Sampling

Question 17

Survivor Sampling

Answer 17

Sample of non-diseased individuals (survivors) at end off study period

Question 18

Base Sampling

Answer 18

Sample of non-diseased individuals at start of study period

Question 19

Risk-Set Sampling

Answer 19

Sample of non-diseased individuals during study period at same time when case was diagnosed

Question 20

Selection Bias

Answer 20

Related to the way subjects are chosen for a study
Always a potential problem
Not too significant in Case-Crossover study designs

Question 21

Recall Bias

Answer 21

Related to the amount/specificity that Cases or Controls recall past events DIFFERENTLY
Usually the Cases are more likely to recall

Question 22

Individual Matching

Answer 22

Matches individuals based on specific patient-based characteristics
Used when each case has unique & important characteristics
1:1

Question 23

Group Matching

Answer 23

Proportion of cases & proportion of controls with identical characteristics are matched
Requires cases be selected first

Question 24

True or False:

You can match for anything, including possible risk factors.

Answer 24

False

Do NOT match for anything that might be a risk factor