Analytical Studies

Question 1

Case control design

Answer 1

• retrospective
• group of cases and controls (diseased and non-diseased)
• then retrospective data on exposure to putative risk factors is collected

Question 2

Causality

Answer 2

-Case control study is often the first step in suspected associations of causality

Question 3

Advantages of case control

Answer 3

• easy
• less time consuming
• less expensive
• suitable for investigating rare diseases
• subjects are not exposed to any new risks
• several etiological factors for a single disease can be studied
• no attritition problems

Question 4

Disadvantages of case control studies

Answer 4

• highly prone to selection and recall bias
• control group selective may be difficult
• incidence cannot be measured-so odds ratio only-no relative risk- can be measured
• cannot prove causality
• temporality is difficult to determine

Question 5

Eligibility criteria

Answer 5

-key in case control studies

Question 6

Power of case control

Answer 6

• up to a ratio of 4:1 when the number of controls is increased, the power of a study increases
• but not after exceeding the ratio

Question 7

Odds ratio

Answer 7

• estimates the risk of exposure
• incidence rates aren’t available so relative risk cant be used
• if the condition is very rare then odds ratio approximates the relative risk
• can have values between 0 and infinity but no negative values
• log transformations are needed to calculate confidence intervals

Question 8

Cohort study

Answer 8

• a cohort is a group of persons sharing a common aspect

- examples are birth cohort or exposure cohort

Question 9

Inception cohort

Answer 9

-a group of patients who are assembled at a single point of time based on a common factor

Question 10

How does a cohort study work?

Answer 10

• exposure cohorts are followed up in parallel with a non-exposed group to detect the development of a disease
• the disease is yet to occur when the study starts

Question 11

Cohort study basic requirements

Answer 11

• easily obtainable, cooperative and stable cohort that can be followed up as needed
• non-exposed control cohort must be comparable to the study cohort in all aspects except the exposure
• they must not have the disease at the time of inception into the study

Question 12

Controls in a cohort study

Answer 12

• Can be internal control or external control
• internal controls are a subgroup of the exposure cohort
• retrospective cohort is allowed

Question 13

Relative risk in cohort studies

Answer 13

• can be calculated as the ratio of the disease (outcome) in the exposed to the disease in non-exposed
• odds ratio can also be calculated

Question 14

Disadvantages of cohort study

Answer 14

• time consuming and difficult
• not suitable for rare diseases
• only one etiological factor can be studied at a time
• attrition/drop out is a major issue

Question 15

Advantages of cohort study

Answer 15

• less prone to selective and recall bias
• incidence can be measured so relative risk can be measured
• causal association can be strongly supported compared to case-control
• temporality is established easily
• multiple effects o a single exposure could be observed
• dose response relationships could be calculated
• natural course of exposure to disease pathway be studied in addition

Question 16

Nested case-control study

Answer 16

• a study in which both the cases and controls are drawn from within a cohort rather than including the entire cohort population in the study
• much cheaper but with the same findings
• case control studies can also be nested within study designs such as cross-sectional studies