Cohort Studies

Question 1

What are the two main types of studies?

Answer 1

Observational and interventional

Question 2

Give an example of interventional studies.

Answer 2

RCTs

Question 3

Given examples of observational studies. (3)

Answer 3

Cohort
Case-control
Cross-sectional

Question 4

How are cohort studies done?

Answer 4

Identify individuals
Measure exposures in each individual
Follow-up individuals to determine disease/disorder occurrence
Relate information on disease occurrence to exposure

Question 5

Explain a cohort study simplistically. (2 words)

Answer 5

Cohort –> disease

Question 6

How do cohort studies differ from case-control studies?

Answer 6

Cohort –> disease FOR COHORT

Exposure

Question 7

Why might there be bias in cohort studies? (3)

Answer 7

Loss to follow-up
Exposure usually measured at just one time point
Selection of cohort

Question 8

What are the disadvantages of cohort studies? (3)

Answer 8

Take a long time
Need a lot of people
Very expensive

Question 9

What was the British Doctors Study?

Answer 9

Information from 34,439 male doctors initially collected in 1951 and they were followed up for 50 years. They were asked about smoking. Death certificates obtained when they died.

Question 10

What is incidence?

What is it usually taken to be a measure of?

Answer 10

Number of new cases (or deaths) of a disease per 100,000 people per year.
Risk

Question 11

How do you calculate relative risk?

Answer 11

Incidence of disease in exposed population/incidence in unexposed population

Question 12

How can we tell if the results have arisen due to chance alone?

Answer 12

Look at p-values and confidence intervals

Question 13

If the risk of a disease is the same for the exposed and for the unexposed populations, what is the relative risk?

Answer 13

1

Question 14

Explain what a 95% CI of a sample relative risk means.

Answer 14

The 95% CI of a sample relative risk contains the population relative risk with a probability of 95%

Question 15

Explain what a 95% CI of a sample mean means.

Answer 15

The 95% CI of a sample mean contains the population mean with a probability of 95%

Question 16

When can you tell that the results (relative risks/ratios) are statistically significant looking at the 95% CI?

Answer 16

If the CI doesn’t include 1 (for means, it is 0 but for risks it is 1).

Question 17

What is a confounder?

Answer 17

A factor that is associated both with the exposure and also with the disease.

Question 18

How do you account for confounders?

Answer 18

Statistical adjustment
e.g. with alcohol and smoking. Analyse alcohol consumption and risk of lung cancer in non-smokers, and alcohol consumption and risk of lung cancer in smokers. You might expect these risks to be similar, in which case you could combine them.

Question 19

Which should you use – unadjusted or adjusted RR?

Answer 19

Adjusted - this is adjusted for confounders.

Question 20

What curves are used for survival analysis? What do these plot?

Answer 20

Kaplan-Meier curves - they plot proportion of people surviving over time.

Question 21

What does the log rank of a Kaplan-Meier curve compare?

Answer 21

The two curves for the exposed/unexposed population

Question 22

How do hazard ratios differ from relative risks?

Answer 22

The take into account the time taken for the event to occur

Question 23

What are hazard ratios?

Answer 23

They give the risk of dying at any time point in one group compared to the other

Question 24

What two measures of importance are given in this lecture?

Answer 24

Absolute excess risk

Attributable proportion

Question 25

How do you calculate the absolute excess risk?

Answer 25

Risk in exposed – risk in unexposed

Question 26

How do you calculate the attributable proportion?

Answer 26

Incidence in population attributable to exposure/incidence in population

Question 27

What is the formula for attributable proportion?

Answer 27

1 + p (RR-1)

where p = proportion exposed in population