Case Control Studies

Question 1

What is a case control study?

Answer 1

an observational study allowing researchers to be a 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 (control)

Question 2

In case control studies, group assignments are based on_______

Answer 2

disease status

Question 3

What are the reasons for a case control design?

Answer 3

• unable to force group allocation (randomize)
• limited resources
• disease of interest is rare
• prospective exposure data is difficult to obtain and/or time inappropriate

Question 4

Case control studies are customarily conducted in _______ fashion

Answer 4

retrospective

Question 5

What are the strengths to a case control study design?

Answer 5

• good for assessing multiple exposures of one outcome
• useful when diseases are rare
• useful in determining association
• less expensive
• useful when ethical issues limit interventional studies
• useful when disease has a long induction/latent period

Question 6

What are the weaknesses of case control studies?

Answer 6

• can’t demonstrate causation
• can be impacted by confounders
• retrospective: can’t control for other exposures
• can be impacted by various biases
• limited by available data

Question 7

What is the selection of cases?

Answer 7

defined by the investigator using accurate, medically reliable, efficient data sources

Question 8

What is the most difficult part of case control studies?

Answer 8

control selection

Question 9

How must controls be selected in a case control study?

Answer 9

irrespective of exposure status

Question 10

What sources can control groups come from?

Answer 10

population
institutional/organizational/provider
spouse/relative/friends

Question 11

Can an individual be an exposed and unexposed individual in the same case control study? If so, how?

Answer 11

Yes in cases with multiple exposures or in a situation of a brief change in risk of the outcome in interest

Question 12

What is a case-crossover design?

Answer 12

subjects are their own controls during the other times they don’t have acute change in risk

Question 13

What is survivor sampling?

Answer 13

sample of non diseased individuals (survivors) at end of study period

Question 14

What is base sampling?

Answer 14

sample of non diseased individuals at start of study period

Question 15

what is risk set sampling?

Answer 15

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

Question 16

What is selection bias related to?

Answer 16

the way subjects are chose for study

Question 17

What is recall bias related to?

Answer 17

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

Question 18

What is matching?

Answer 18

When cases are matched to controls (either 1:1 or higher ratio)

Question 19

What is individual matching?

Answer 19

matches individual based on specific patient based characteristics, useful to controlling confounding characteristics

Question 20

What is group matching?

Answer 20

promotion of case and proportion of controls with identical characteristics are matched, case must be selected first

Question 21

You should not match anything that might be a ______

Answer 21

risk factor