POPH192 - Lecture 20

Question 1

what type of study is a case control study?

Answer 1

analytic and obversational

Question 2

how do case control studies work?

Answer 2

the work backwards
- start with participants with a known outcome status

Question 3

first step of a case control study?

Answer 3

1) identify a source population

Question 4

second step of a case control study?

Answer 4

2) identify the cases (people with outcome) and controls (people without outcome)

Question 5

third step of a case control study?

Answer 5

3) assess their prior exposure level in cases and controls

Question 6

fourth step of a case control study?

Answer 6

4) calculate odds ratio

Question 7

which calculations can you solve from case control studies

Answer 7

odds ratio only

Question 8

what are important things to consider for case control studies?

Answer 8

• index date
• selection of cases
• purpose of control group
• controls
• control selection
• measuring exposure
• bias

Question 9

what is important about the index date?

Answer 9

it can be used for transient exposures in controls who didn’t have an associated event
- the exposure is measured on the same date as the case

Question 10

what is important when selecting cases?

Answer 10

there needs to be a clear definition of the outcome and cases should be newly incident

Question 11

what is the purpose of having a control group?

Answer 11

to represent the exposure distribution in source population

Question 12

what is an important thing that controls should be capable of?

Answer 12

should be capable of becoming a case and often we select multiple controls per one case for better statistical power

Question 13

what are one of the ways to select a control and what is the problem with this?

Answer 13

can select controls from a hospital
- using hospital based controls can cause problems as they aren’t necessarily representative of the population which the cases came from (they may have diseases which are also related to the exposure being studied)

Question 14

what do you need to ensure when measuring exposure?

Answer 14

need to ensure that exposure is measured before the outcome so that we have temporal sequence

Question 15

what can measuring exposure allow potential for?

Answer 15

when measuring exposure level in a case control study, there is potential for information bias (recall and interviewer bias)

Question 16

what are the strengths of a case control study?

Answer 16

• good for rare outcomes and transient exposures
• can assess multiple exposures
• temporal sequencing
• quick and inexpensive compared to other studies

Question 17

what are the limitations of the case control studies?

Answer 17

• can only study one outcome
• difficult to select an appropriate control group
• prone to selection and recall bias