Statistics

Question 1

Effect modification

Answer 1

o Definition = Effect of an exposure on an outcome is modified by another variable. NOT a bias.
o Example: A study showing a new drug increases the risk of DVT in treated women who smoke compared to untreated women who smoke, with an RR of 1.7. In nonsmokers, no increased risk of DVT is evident with use of the drug.
o Other notes: You can resolve this problem with STRATIFICATION. Ie in an analysis of primary school students, age can be a confounder that muddles the association between shoe size and intelligence. Children with bigger shoe sizes may appear to be more intelligent on initial analysis. When older and younger children are stratified, the association between shoe size and intelligence disappears.

Question 2

Rare disease bias effect

Answer 2

odds ratio approximates RR

Question 3

Determining significance of relative risk…

Answer 3

If 1.0 falls within the presented interval, then the relative risk is not significant. If 1.0 does not fall within the interval, then the presented relative risk is significant.

Question 4

How do you calculate a type II error?

Answer 4

Type 2 error = 1 - Power

Question 5

Example of a type II error

Answer 5

Indicating a drug does not work when it really does.

Question 6

Type 1 (alpha error) statistical definition

Answer 6

Null hypothesis is rejected when it is really true.

Question 7

Type 2 (beta error) statistical definition

Answer 7

You fail to reject the null hypothesis when it is really false. (indicating a drug doesn’t work when it really does)

Question 8

How do you determine if null hypothesis is rejected?

Answer 8

If the p value is greater than the alpha criterion (usually 0.05), null hypothesis is not rejected. If it’s less than 0.05, the null hypothesis is rejected and statistical significance is proven.

Question 9

state confidence interval equation

Answer 9

ok

Question 10

How to approach problems about changing threshold…

Answer 10

Think about how test will work in new population at large.

Question 11

Affect of lowering a threshold…

Answer 11

• Increase NPV.

* Increase sensitivity.

Question 12

Case series design

Answer 12

Collects detailed information about people who are all believed to have the same disease or condition. Intended to describe common elements defining the disease.

Question 13

Cross sectional study assesses…

Answer 13

PREVALENCE.

Question 14

statistics tool for cross-sectional study

Answer 14

Chi-square analysis