case control studies

Question 1

analytic studies catchphrase

Answer 1

Does the exposure increase or decrease the risk of the outcome?

Question 2

what are the case controls designed to test

Answer 2

Designed for rare/slow to develop outcomes
Can efficiently examine acute or transient exposures

Question 3

what are the 5 steps involved in making a case control

Answer 3

1: identify a source population
2: identify people in the source population with the outcome
3: sample people in the same population who do not have the outcome
4: measure exposure status prior to outcome in the cases and controls
5: calculate the odds of exposure in the groups and then use these numbers to find OR.

Question 4

whats the logic of a case control study

Answer 4

Is the exposure more or less likely in people with the outcome (cases) than without (controls)?

Question 5

how do we go about getting our population for a case control study

Answer 5

Case control: find people with the outcome and find those who don’t have the outcome. IN THE SAME POPULATION. Then we define people based on their exposures.

Question 6

whats most important aspect of case controls and why

Answer 6

taking the cases and controls from the same study. by taking everyone from the same population we know that they are all exposed to similar things daily. this makes it more easy to define people based on one exposure alone

Question 7

why do we have the control sample ?

Answer 7

The control sample of the population exists to provide a normal baseline of the outcome for the everyday people who be not exposed.

Question 8

why cant we measure prevalence and incidence in case control

Answer 8

We cant calculate incidence as we don’t have a defined time period. We also selected the people in the study on purpose based on their outcome status.
so we cant measure prevalence as we purposely selected cases

Question 9

how do we calculate the odds of exposure on each group

Answer 9

case exposed control exposed
——————- ————————–
case not Exp control not exp

Question 10

what measure do we use for case control studies

Answer 10

we use the measure of association: odds ratio

Question 11

whats the null value for odds ratio

Answer 11

The null value for this is 1. what does this mean. there is no association between outcome and exposure, as both groups are as likely to have had exposure as each other

Question 12

how do we report odds ratio

Answer 12

People with outcome are x
times as likely to have had the
exposure than people without
the outcome

Question 13

describe index dating

Answer 13

To combat this we use index dates. We take dates of another persons diagnosis and find controls at the same time. In the time before that is when we measure the exposures of people.

Question 14

case-control studies are defined by outcome this means?

Answer 14

only one outcome measured per study, Really important clearly defined and readily identifiable

Question 15

whats important in selecting people to case controls

Answer 15

We must represent the exposure distribution of people without the outcome in the source population. The people who are the control cases within this population must have the ability to become a case themselves.

Question 16

whats a hospital control and why aren’t they the best

Answer 16

Hospital cases: controls taken from people in hospital due to having other outcomes. These people in hospital are easy to access and identify. However they may not be the best option as the exposure of their outcome may be similar to the exposure of the defining out come of the study.

Question 17

cons of dead cases vs alive controls

Answer 17

The dead cases arent always accurate as we have to rely on exposure reccounts from people who arent the ones with the outcome.

Question 18

what does recall ability impact

Answer 18

Physically with head trauma. But people may change attitudes after outcome.

Question 19

strengths of case control

Answer 19

Rare outcomes, transient exposures, Multiple exposures, Temporal sequencing, Often comparatively quick and inexpensive

Question 20

Limitations of case control

Answer 20

Usually can only study one outcome, Difficult to select appropriate control group, Can be susceptible to selection and recall bias