Epidemiology

Question 1

What is a cohort study?

Answer 1

Observation of large numbers of people over a long period with comparison of incidence rates in groups that differ in exposure levels

Question 2

Advantages of cohort studies

Answer 2

• incidence rates and relative risks
• avoid bias in determining effects
• can investigate more than one disease

Question 3

Disadvantages of cohort studies

Answer 3

• large number of participancts and long follow up
• costly
• possible bias in disease discovery
• only representative of cohort selected

Question 4

What is relative risk?

Answer 4

probability of having a disease among one group / probability of having a disease among unexposed individuals

Question 5

What is a case-control study?

Answer 5

start by knowing who has the disease and work back to find who was exposed

Question 6

What is matching used for?

Answer 6

to control for confounding factors such as age, sex, geographical area

Question 7

Disadvantages of matching

Answer 7

• exclusion of cases if match not found
• longer study duration

Question 8

Odds

Answer 8

probability of having a disease / probability of not having the disease

Question 9

Odds Ratio

Answer 9

odds in one group / odds in other group

Question 10

What is an ecological study?

Answer 10

a study in which the units of analysis are populations rather than individuals

Question 11

Advantages of ecological studies

Answer 11

• use publicly available data
• cheap and quick
• can study large populations

Question 12

Disadvantages of ecological studies

Answer 12

• difficult to infer causation
• susceptible to bias and ecological fallacy

Question 13

What is ecological fallacy?

Answer 13

incorrect assignment of individual exposures based on aggregate level

Question 14

What is a cross-sectional study?

Answer 14

a study which examines the relationship between diseases and other variables of intrest as they exist in a defined population at one particular time point

Question 15

Advantages of cross-sectional studies

Answer 15

• cheaper
• one time point, one data collection point
• can estimate prevalance rates

Question 16

Disadvantages of cross-sectional studies

Answer 16

• only representative of study sample
• not effective if disease is rare
• may not be representative of all cases

Question 17

What is a nested case-control study?

Answer 17

cases and controls drawn from a cohort study

useful to adjust for confounding effect of time