Modules 10 and 11 - Cohort, Case Control, and Surivival Studies

Question 1

What are the strengths of a case control study?

Answer 1

1. Disease is rare 2. Exposure is frequent among diseased 3. Helps to indicate a relationship between disease and exposure

Question 2

What are the weaknesses of a case control study?

Answer 2

1. Selection of inappropriate controls 2. Incomplete information or exposure 3. Recall bias

Question 3

What are two outcome measures in a case control study?

Answer 3

Proportion of cases exposed; proportion of controls exposed

Question 4

What is the measure of risk used in a case control study?

Answer 4

Odds ratio

Question 5

Why isn’t relative risk used to measure risk in case control studies?

Answer 5

Because one is selecting patient based on OUTCOME (disease)

Question 6

No carcinogen/cancer = 84 Carcinogen/cancer = 16 No carcinogen/no cancer = 96 Carcinogen/no cancer = 4 Calculate the odds ratio.

Answer 6

Odds of exposure to carcinogen WITH cancer = 16/84 = Odds of exposure to carcinogen WITHOUT cancer = 4/96 (16/84)/(4/96) = 4.6

Question 7

If relative risk obtained from a cohort study is NOT significant, what might be a 95% confidence interval? A. (.40, .95) B. (.15, .35) C. (.75, 1.10)

Answer 7

C. A relative risk of 1 means “no association”, and this interval crosses 1.

Question 8

a) Identify the study design:

Defined population; Nonrandomized;

Split into exposed/non-exposed

b) Is this analytical or descriptive?
c) Is this an experimental trial or and observational trial?

Answer 8

a) Cohort
b) Analytic
c) Observational - exposure variable not manipulated by investigator

Question 9

What are strengths of the cohort study?

Answer 9

Strengths - rare exposures, temporal relationships, determine rate of disease outcome

Question 10

What are the outcome measurements of a cohort design (and the measurements of risk)?

Answer 10

1. Outcome measurement: incidence exposed + incidence nonexposed
2. Measurement of risk:Absolute and relative riskOdds ratio (but OR is better for case control studies)

Question 11

What are the weaknesses of a cohort study?

Answer 11

Weaknesses - long follow-up, hard to investigate rare diseases, no randomization, no casual relationship, cost, confounders

Question 12

Calculate the relative risk:

Answer 12

RR = (clot+/BC+)/(clot+/BC-) = 4.

Question 13

Answer 13

A

Question 14

Calculate the odds ratio:

Answer 14

Odds that case was exposed/odds that control was exposed = 4.44

Question 15

Which is NOT a correct difference between RR and OR?

A. OR can be calculated for both case control and cohort studies but RR can be used only for cohort studies.

B. Odds ratio over-estimates relative risk when the disease is common.

C. Relative risks can be multiplied directly and odds ratios can not.

D. Relatives risks change depending on whether the outcome is developing the disease or not developing the disease, but OR do not.

Answer 15

C

Question 16

When is an odds ratio similar to relative risk?

A. When the disease is rare

B. When there is no recall bias

C. When there are more exposed than not exposed people

D. When there are no confounders

E. When case control study is done

Answer 16

A