Case-Control Studies

Question 1

1) What are case-control studies useful for studying? 2) What do Case-control studies commonly generate?

Answer 1

1) Rare diseases *** and investigating outbreaks 2) Odds of exposure for both cases and controls then uses them for OR

Question 2

What are some reasons to use case control studies?

Answer 2

• unable to force group allocation (unethical) - limited resources (time, money, subjects) - dz of interest is rare - prospective exposure data is difficult/expensive to obtain

Question 3

Are case control studies retrospective or prospective?

Answer 3

Retrospective (usually)

Question 4

What are some strengths for case control studies?

Answer 4

• assessing multiple exposures of ONE outcome - can study rare dz’s - determining associations (NOT causations) - less expensive/time consuming - for dz with long latency periods

Question 5

What are some weaknesses for case control studies?

Answer 5

• can’t demonstrate causation - impacted bu unassessed confounders - retrospective so can’t control for other exposures or potential changes - impacted by biases – Selection and Recall - limited by data

Question 6

Whats the number one option for selection of cases?

Answer 6

• Use a case definition - be as objective, consistent, accurate, with reproducibility and validity

Question 7

Controls MUST be selected irrespective of their ________.

Answer 7

Exposure status - cannot match them on exposure bc then the OR would be one

Question 8

What are 3 ways controls can be selected?

Answer 8

1) Population 2) Institutional 3) Family

Question 9

Always want to put a _____ on exposure when looking for controls.

Answer 9

Blinders

Question 10

Can an individual fnx as both an exposed individual AND and unexposed individual in the same study at the same time?

Answer 10

YES - can be assoc with an outbreak investigation with multiple exposures - in a situation of a brief change in risk of the outcome of interest – a case-crossover design

Question 11

• In a Case-crossover study the controls act as ______. - They can demonstrate what?

Answer 11

• their own controls - temporality (is the risk factor/exposure associated with the dz?)

Question 12

What are nested case control studies?

Answer 12

Case control studies that come out of a previous prospective study (cohort or interventional) - used to evaluate other exposures

Question 13

How are samples collected for nested control studies?

Answer 13

1) survivor sampling = subjects who don’t have the dz at the end of the study 2) base sampling = subjects who don’t have the dz at the beginning of the study 3) Risk-set sampling = time based sampling where non-dz ppl are selected when the cases were dx

Question 14

What are the two common biases for case-control studies?

Answer 14

Selection bias = related to the way subjects are chosen for study

• less concern during Case-crossover study designs

Recall bias = related to the amount/specificity that cases or controls recall past events DIFFERENTLY

Question 15

What is individual matching?

Answer 15

Matches individuals based on specific pt-based characteristics

• useful for controlling confouding charac

Question 16

What is group matching?

Answer 16

Proportion of cases and proportion of controls with ID characteristic are matched

• ex = 41% of cases are male and 41% of controls are male
• cases must be selected first

Question 17

DON’T match anything that might be a _______.

Answer 17

Risk factor