POPH192 Lecture 20 - Case Control Studies

Question 1

are case-control studies an observational or an intervention study?

Answer 1

observational study

Question 2

what are case-control studies designed for?

Answer 2

designed for rare/slow to develop outcomes

Question 3

what do case-control studies examine?

Answer 3

can efficiently examine acute or transient exposures

Question 4

what do case-control studies ascertain?

Answer 4

ascertain outcome status, then find out exposure(s)

• outcome to exposed?
• no outcome to exposed?

Question 5

what are the 5 steps of creating a case-control study?

Answer 5

1) identify source population
2) identify people with the outcome (cases)
3) sample people without outcome from same population (controls)
4) measure exposure prior to outcome in cases and controls
5) compare odds of exposure to calculate measure of association: odds ratio (odds of exposure (cases)/ odds of exposure (controls)

Question 6

what does it mean if the cases and controls are a good representation of the source population?

Answer 6

ratio of odds of exposure quantifies association between exposure and outcome

Question 7

what does it mean if exposure is more likely in cases?

Answer 7

exposure is a potential risk factor

Question 8

what does it mean if exposure is more likely in controls?

Answer 8

exposure is a potential protective factor

-exposure is not always bad

Question 9

what does transient exposure measure?

Answer 9

only measures the relevant exposure period

Question 10

what is the null value for the odds ratio?

Answer 10

1

Question 11

when does the odds ratio (OR) approximately equal the relative risk (RR)?

Answer 11

when disease is rare, OR approximates the relative risk (rare disease assumption)v
-can interpret just like RR

Question 12

what is the statement used for interpreting the odds ratio?

Answer 12

the EXPOSED GROUP were VALUE as likely to develop OUTCOME compared to COMPARISON GROUP

Question 13

can controls measure the outcome?

Answer 13

controls don’t have outcome therefore they can not measure exposure

Question 14

how case-control studies measure exposure?

Answer 14

index dates

Question 15

what are index dates?

Answer 15

pretend control had event on the same date as the case (or at least close to it)

Question 16

what are the 3 important points of case-control studies?

Answer 16

1) defined by outcome, so only one outcome
2) clear outcome defintion and identification
3) comprehensive case finding

Question 17

do case-control studies use incidence or prevalent cases?

Answer 17

usually try to identify with incident cases

Question 18

what are the 2 most important things for

control selection to be valid?

Answer 18

• need to represent the exposure distribution in source population
• must be capable of becoming a case (important for a control)

Question 19

what are the limitations of a case-control study?

Answer 19

• usually can only study one outcome
• difficult to select appropriate control group
• can be susceptible to selection and recall bias

Question 20

what are the strengths of a case-control study?

Answer 20

• rare outcomes, transient exposures
• multiple exposures
• temporal sequencing
• often comparatively quick and inexpensive