Epi - L3 - Case Control Studies

Question 1

what is a Case-Control study?

Answer 1

it is an OBSERVATIONAL study that allows researchers to be passive observers of natural events occuring 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

What doe the control group supply?

Answer 2

it supplies info about the expected baseline risk-factor profile in the population from which the cases are drawn

Question 3

what is the group-assignment based on?

Answer 3

disease status

Question 4

when are case-control studies useful?

Answer 4

when studying a rare disease or investigating an outbreak

Question 5

what are the reasons you’d select a Case-Control design?

Answer 5

1. unable to force group allocation (randomize)
   
   • unethical/ not feasible
2. limited resources (time/ money/ people)
3. the disease of interest is rare and little is known about its associations/ causes
4. prospective exposure data is difficult/ expensive to obtain and/ or very time inappropriate (*any study where we know the outcome BEFORE the exposure)

Question 6

are case-control studies customarily conducted in a retrospective or prospective fasion?

Answer 6

retrospective; so this means we go back and look at the collected data already. it saves time and resources

so if you know the outcome before the exposre, it means youre looking at a case-control study

Question 7

are interventional studies prospective or retrospective?

Answer 7

prospective

Question 8

what are some strengths of Case-Control studies

Answer 8

• good for assessing multiple exposures of one outcome
• useful when diseases are rare
• useful in determining associations (NOT causations)
• less expensive
• useful when ethical issues limit interventional studies
• useful when a disease has a long induction/ latent period

Question 9

what are some weaknesses of case-control studies

Answer 9

• cant demonstrate causation
• can be impacted by unassessed confounders
• retrospective; can’t control for other exposures or potential changes in amount of study-exposure during study frame
• can be impacted by selection and recall biases
• limited by available data (retrospective nature)

Question 10

how do you select cases?

Answer 10

defined by the investigator using accurate, medically-reliable, efficient data sources
applied to all subjects:
- objectively, consistently, accurately, and with validity

Question 11

What is the goal of selecting controls?

Answer 11

the goal is to assess for the presence of an association between exposure and unknown condition of interest by selecting non-disease individuals form the sample population which produced the Cases

Question 12

what is the expectation of the controls?

Answer 12

that it will represent the baseline risk of exposure in the general or reference population

Question 13

how do you select the Control study population?

Answer 13

we want groups to be as equal as possible EXCEPT the presence of disease (outcome) of interest

*if the exposure truly has no effect, then odds will be exactly the same for both groups and OR will be 1.0 (no difference)

**controls must be selected irrespective of exposure status!!

Question 14

exposed and unexposed

Answer 14

an individual can function as BOTH an unexposed individual AND an exposed individual in the same study

• can be associated with an outbreak investigation or can be in a situation of acute change in risk of outcome in interest

Question 15

what is that previous thing called?

Answer 15

Case-Crossover design

• subjects are their own Controls
• the only Case-Control design able to adequately attempt to address issue of temporality

Question 16

What is a nested Case Control study?

Answer 16

These are Case-Control studies conducted after, or out of, a prospective previous study-type (cohort or interventional study)

• subjects in cohort study, ultimately developing disease/ outcome, are defined as cases for the subsequent Case-Control study
• nested: a study that comes out of another study

Question 17

where do you find the controls in a nested study?

Answer 17

within the case-control study you’re ‘nesting’ from.

Question 18

what are the type of samplings?

Answer 18

1. SURVIVOR sampling - sample of non-diseased individuals at the end of study period
2. BASE - sample of non-diseased individuals at start of study
3. RISK-SET - sample of non-diseased individuals during study period at same time when Case was diagnosed

Question 19

what are the common biases in Case-Control?

Answer 19

selection bias (less concern during case-crossover study, more concern for Control selection)

recall bias

Question 20

Matching

Answer 20

= in some studies, cases are matched to controls (individual or group matching)

• individual - matches individuals based on specific patient-based characteristics *useful for controlling confounding characteristics)
• group - proportion of cases and proportion of controls with identical characteristics are matched *requires cases to be selected first

**DON’T match on anything that might be a risk factor!