Trials and Research Methods

Question 1

What is the difference between prevalence and incidence?

Answer 1

Prevalence - Ratio of persons affected and frequency within a single time point Incidence - Ratio of persons in whom the disease develops within a specified period

Question 2

Is prevalence or incidence more useful for discussing diseases of longer duration?

Answer 2

Prevalence

Question 3

What is the difference between odds ratio and relative risk?

Answer 3

Relative risk - risk of event in treatment group compared with control:

a/a+b vs c/c+d

Odds ratio - odds of event in treatment group compared with control

a/b vs. c/d

Question 4

What are 3 types of bias?

Answer 4

1. Selection bias (e.g. healthier or sicker patients self select to volunteer for studies)
2. Information bias (e.g. recall bias)
3. Confounding

Question 5

What is a type 1 statistical error?

Answer 5

Rejecting the null hypothesis when it actually is true - typically set Alpha = 0.05

Question 6

What is a type 2 statistical error?

Answer 6

Not detecting a difference when one truly exists (i.e. failure to reject null hypothesis when it is false). Beta usually 0.8. Power = 1 - beta.