36. COHORT STUDIES

Question 1

1. What is initially selected during Cohort Studies?

Answer 1

• a random sample
• this comes from the source population

Question 2

2. What happens before we initiate the Cohort study?

Answer 2

• all the patients that suffer from the disease are
  excluded

THE SAME APPLIES TO LARGE EPIDEMIOLOGICAL STUDIES:
- where all of the individuals that are suffering from any
kind of disease are excluded

Question 3

3. What happens when the Cohort Study is Initiated?

Answer 3

• this is known as the Study Baseline

ALL OF THE EXPOSURES OF INTEREST:
- and all of the potential confounders
- are assessed

Question 4

4. What happens after all of the exposures of interest have been assessed in a Cohort Study?

Answer 4

• the participants will continue to live their lives normally
• the researchers will then record new cases of the
  disease during the Follow Up

Question 5

5. During Cohort Studies, how are the new disease cases ascertained?

Answer 5

THEY COME FROM:
- Clinical examinations
- this is the most preferred measures

• hospital registries
• national registries
• self-reports

NB:
- they come in specific time intervals
- usually every 2 to 3 years

Question 6

6. What is the main aim of Cohort Studies?

Answer 6

• to investigate whether the incidence (risk) of different
  diseases will differ
• this difference will be based on different exposures
• they look at the exposed and the unexposed groups

Question 7

7. What kind of study is a Cohort study, when we look at the relation of the exposure to the outcome?

Answer 7

• it is a Prospective study
• this is due to the time lapse between the exposure and
  the outcome

Question 8

8. What are the Descriptive Measures related to Cohort Studies?

Answer 8

1. INCIDENCE
   - this deals with Binary Variables
2. MEAN AND MEDIAN
   - this deals with Numeric Variables

NB:
- descriptive measures are very rarely recorded in
Cohort Studies

Question 9

9. What are the Measures of Association related to Cohort Studies?

Answer 9

1. RISK RATIO:
   - this deals with Binary Categorical Outcomes
2. RATE RATIO:
   
   • this deals with Binary Categorical Outcomes
   • it is used when we can calculate the Person Years
3. MEAN DIFFERENCE:
   - this deals with Categorical Exposures
   - that have Numeric Outcomes
4. ODDS RATIO:
   - this can be calculated when the Binary Outcome us
   very rare

Question 10

10. What are the advantages of Cohort Studies?

Answer 10

1. IT IS POSSIBLE TO ASSESS THE RISK (INCIDENCE)
   - and the mortality of the disease
   - this allows us to calculate the Relative Risk
2. IT MAKES IT POSSIBLE TO ASSESS TEMPORAL
   ASSOCIATIONS
   - this helps to prove that the exposure preceded the
   outcome
3. IT MAKES IT POSSIBLE TO ASSESS SEVERAL
   EXPOSURES AND OUTCOMES
   - this provides more valid and informative results
4. IT MAKES IT POSSIBLE TO INVESTIGATE RISK FACTORS
   - for Chronic Diseases
   - these take years to develop and can be seen in the
   follow up
5. THE STUDY SAMPLES ARE LARGE
   - this increases the Internal Validity
   - by decreasing the Random Error

Question 11

11. What are the disadvantages of Cohort Studies?

Answer 11

1. THEY HAVE AN OBSERVATIONAL DESIGN
   
   • they are prone to Information Bias
   • this is because most of the measurements are based
     on self reports and questionnaires
2. THEY HAVE AN OBSERVATIONAL DESIGN
   - this is because it is not always possible to assess all
   the potential confounders
3. IF WE HAVE PARTICIPANTS THAT SELECTIVELY DROP
   OUT OF THE STUDY
   - there becomes a risk of Selection Bias
4. IT IS VERY DIFFICULT TO ASSESS THE RISK (INCIDENCE)
   OF A RARE DISEASE
   - since we need very large samples
5. IT IS DIFFICULT TO CONDUCT THIS KIND OF STUDY
   - because of the huge costs of it
   - and the long duration time
6. IT IS DIFFICULT TO PROVE THE CAUSALITY IN THE
   STUDY
   - this is due to the possible biases
   - it is also due to Confounding
   - this is less prevalent in this study design compared
   to other Observational Study Designs