Case Control Studies

Question 1

Cases that present are compared with one or more _______

Answer 1

Controls

- comparands: animals without the disease

Question 2

Case control studies are ______

Answer 2

Retrospective

• compare frequency of occurrence of exposures/risk factors
• look at multiple risk factors to detect which ones are more or less seen in cases, and may be causal
• quickly done with low cost

Question 3

Can case control studies be done to study rare or infrequent diseases?

Answer 3

Yes!

Question 4

What is the measure of association for a cohort study?

Answer 4

Relative risk

- risk of disease in exposed/risk of disease in unexposed

Question 5

What is the measure of association for a case control study?

Answer 5

Odds ratio

- odds of exposure in cases compared to odds of exposure in non-cases

Question 6

Both, odds ratio and relative risk, measure ______

Answer 6

Strength of association between exposure and disease

Question 7

What is the probability of an event occurring to the probability of the event not occurring?

Answer 7

Odds

Question 8

Odds ratio and relative risk are pretty close when the disease is ______

Answer 8

Rare

Question 9

Could odds ratio be used as the measure of association in cohort studies?

Answer 9

Yes, but relative risk is easier to communicate

Question 10

Odds of exposure within cases

Answer 10

Disease present = number exposed/number unexposed

Question 11

How to describe odds ratio?

Answer 11

The odds of exposure in the cases is ____, compared to the odds of exposure in non-cases
- the odds of exposure in cases is ____ times that of non-cases

Question 12

Cross product ratio

Answer 12

Way to calculate odds ratio

- (ad)/(bc)

Question 13

Odds ratio > 1 indicates

Answer 13

An increased risk of exposure to new cases

Question 14

Odds ratio = 1 indicates

Answer 14

There is no increased risk

- no relationship between being a case and being exposed

Question 15

Odds ratio < 1 indicates

Answer 15

Sparing effect

Question 16

Can odds ratio go below zero?

Answer 16

No! It could theoretically go to infinity

- the bigger the number, the stronger the relationship

Question 17

Odds ratio approximates relative risk if disease is _______

Answer 17

Rare in population (usually thought as <10%)

Question 18

Can relative risk be used in case control studies?

Answer 18

No

Question 19

Which study: OR is measure of association and OR estimates risk of exposure in cases compared to exposure in controls?

Answer 19

Case control

Question 20

Which study: RR is effect measure, RR estimates risk of disease in exposed, compared to risk of disease in non-exposed

Answer 20

Cohort

Question 21

Factor A occurs before disease X

Answer 21

Temporal relationship

- factor A causes disease X

Question 22

Factor A is present very often in cases, and not in controls

Answer 22

Strength of association

- factor A causes disease X

Question 23

Based on what is known, factor A could cause disease X

Answer 23

Biological plausibility

- factor A causes disease X

Question 24

What are 7 conditions that would cause factor A causing disease X?

Answer 24

• temporal relationship
• strength of association
• biological plausibility
• dose response relationship
• consistency of multiple studies
• rule out other possible causes
• reversible associations

Question 25

Cross sectional

Answer 25

A population of animals is sampled at a specific point in time

• snapshot of population
• prevalence study
• asses absolute risks in the population

Question 26

With a cross sectional study, each animal is classified according to _____

Answer 26

Status of outcome and risk factor, simultaneously, at the time of the snapshot

Question 27

Are temporal relationships established with a cross sectional study?

Answer 27

No, difficult to establish

- look at strength of association of risk factor and outcome