20-21 Case Control Studies

Question 1

Define case.

Answer 1

A person with a disease of interest.

Question 2

What are case control studies?

Answer 2

observational and analytical

allows researchers to be a passive observer of natural events occurring in cases compared with controls

group assignments are based on disease status

useful when studying a rare disease or investigating an outbreak

study differences in exposure

Question 3

List reasons not to select a case-control study.

Answer 3

Unable to randomize

limited resources

the disease of interest is rare in occurrence and little is known about its associations/causes

prospective exposure data is difficult to obtain and/or very time inappropriate

Question 4

List the strengths of case control studies.

Answer 4

good for assessing multiple exposures of one outcome

useful when diseases are rare

useful in calculating odds and odds ratios (associations)

less expensive than interventional trials and prospective cohort studies

useful when ethical issues limit interventional studies

useful for dynamic populations

useful when diseases has a long induction/latent period

Question 5

How are cases selected?

Answer 5

by the investigator using accurate, medically-reliable, and efficient data sources

Question 6

How does the researcher apply the selection process to the study participants?

Answer 6

objectively, consistently, accurately, and with validity

Question 7

What is the best criteria for case selection?

Answer 7

clinically supportable and definable

Question 8

What do we worry about with case selection?

Answer 8

misclassification

Question 9

True or False, control selection is easier than case selection.

Answer 9

False, control selection is harder than case selection.

Question 10

True or False, the way the controls are selected is a major determinant in whether any conclusion is valid.

Answer 10

True

Question 11

What sources can the control group come from?

Answer 11

population

institutional/organizational/provider

spouse/relatives/friends

outbreak: other participants of the event

Question 12

True or False, an individual can actually function as both a case and a control in the same study.

Answer 12

True

Question 13

How can an individual can actually function as both a case and a control in the same study?

Answer 13

Can be associated with an outbreak investigation with multiple exposures

in a situation of a brief (acute) change in risk of the outcome in interest (hazard period)

Question 14

What are nested case control studies?

Answer 14

These are case control studies conducted after, or out of a prospective cohort study.

Question 15

What are the different types of sampling of controls?

Answer 15

Survivor, base, and risk-set sampling

Question 16

What is survivor sampling of controls?

Answer 16

Sample of non-diseased individuals at the end of the study period.

Question 17

What is base sampling of controls?

Answer 17

sample of non-diseased individuals at the start of the study period.

Question 18

What is risk-set sampling of controls?

Answer 18

sample of non-diseased individuals during the study period at the same time when the case was diagnosed.

Question 19

What is selection bias?

Answer 19

related to the way subjects are chosen for study

Question 20

What is recall bias?

Answer 20

related to the amount/specificity that cases or controls recall past events differently

Question 21

List and describe the 2 matching schemes for case control studies.

Answer 21

Individual: matches individuals based on a specific patient-based characteristics

Group: proportion of cases & proportion of controls with identical characteristics are matched

Question 22

Where does nested case-control studies get their controls?

Answer 22

They go back to the cohort study and pull their controls from there.

Question 23

How are case-control studies setup?

Answer 23

based on outcome, looking for exposure

Question 24

Define bias.

Answer 24

any factor in the design/execution of a study that causes study groups to different which ultimately leads to a spurious association between variables

Question 25

True or false, selection bias is less of, or not, a significant issue during Case-Crossover study designs.

Answer 25

True