Biostats

Question 1

How do you calculate Confidence intervals?

Answer 1

Confidence interval of the mean (CI) = sample mean ± Z x SD/√n

For 95% confidence interval for the mean: Z-score = 2

For 99% confidence interval for the mean: Z-score = 2.5

Question 2

Explain a Type II error and how to calculate it?

Answer 2

A Type II error (beta error) is committed when researchers fail to reject the null hypothesis when it is really false. (The researchers declare no significant effect on the basis of the sample when there really is one in the population. For example they indicate that a drug does not work when it really does. NOTE: The chance of a type II error cannot be directly estimated from the p-value.)

The chance of a type II error cannot be directly estimated from the p-value; however, it can be calculated using the following equation: 1-Power = Type II error.

Question 3

What is Number Needed to Treat and how do you calculate it?

Answer 3

Number of individuals that need to be treated to prevent a negative outcome in one patient

NNT = 1/ARR

ARR = control rate - treatment rate

Question 4

What is the point of a case control study?

Answer 4

compare the exposure of people with the disease (cases) to the exposure of people without the disease (control). The main measure of association is the exposure odds ratio