Epidemiology and Stats

Question 1

Properties of the distribution of sample means

Answer 1

Mean of all sample means will be equal to population mean
Standard deviation of all sample means is called the Standard Error
Given a large enough sample size the distribution of sample means will always be normal

Question 2

Equation for Standard Error of a study sample

Answer 2

SE = SD/root(N)
SD is standard deviation of sample
N is size of sample

Question 3

Properties of Standard Error

Answer 3

Large means measurement is imprecise
Small means estimate is precise
As sample size increases SE gets smaller

Question 4

Confidence Interval

Answer 4

Range of values in which the population parameter is likely to lie

Question 5

Calculation of 95% CI

Answer 5

X+- 1.96xSE

Where X is the sample parameter (like mean0

Question 6

Lack of significance in CI

Answer 6

If a CI for a difference includes zero it is insignificant

If a CI for a ratio includes 1 it is insignificant

Question 7

Type 1 Error

Answer 7

Rejecting the null hypothesis when it is true
(Thinking data is significant when P is greater than Alpha)
Significance level of Alpha is probability of making a type I error
P=.05, Prob of type 1 error is 5%
False Positive Rate

Question 8

Type II Error

Answer 8

Inability to reject the null hypothesis even when the data is actually significant
Denoted by B

Question 9

Power

Answer 9

1-B
The chance of obtaining a statistically significant p-value when the null hypothesis is truly false
False negative rate