Case-control Studies

Question 1

Classification of participants

Answer 1

Participants are classified according to disease and investigator determines exposure to calculate OR

Question 2

Usefulness of case-control studies

Answer 2

Used for rare diseases with relatively long latent periods

Question 3

Control group

Answer 3

Represents average exposure from where the participant comes from

We would find him/her if he/she becomes a case

Question 4

Advantages

Answer 4

• Good for RARE diseases
• Several exposures can be studied using 1 outcome
• Long latent periods can be studied
• More efficient than prospective cohort studies
• Economic/Efficient o Fast
• Multipurpose

Question 5

Disadvantages

Answer 5

• Different motivations: controls are less likely to participate so more difficult to obtain sample
• Cannot calculate incidence - follow up is implicit

Question 6

Neyman fallacy of survival bias

Answer 6

Selection bias where the very sick or very well (or both) are erroneously excluded from a study

Excluding patients who have died will make conditions look less severe

Degree of exposure determines prognosis -> retrospective case-control study uses only mild cases (severe ones have died) and leads to underestimation of odds of exposure in cases and OR. It can be avoided by using a prospective case-control study with variety of severity among cases

Question 7

Recall bias

Answer 7

Systematic error that occurs when participants can’t remember/don’t tell you past exposures

• Cases are more likely to give exposure information

Question 8

Berkson bias

Answer 8

When sample is selected from hospital rather than community so there will be overestimation of odds of exposure in cases and OR