Flashcards in Biostats Deck (34):

0

## What is the equation for sensitivity?

### TP/(TP+FN)

1

## What does 100% sensitivity indicate?

### Low false negative rate

2

## What is sensitivity used for?

### Used for screening in diseases with low prevalence

3

## What is the equation for specificity?

### TN/(TN+FP)

4

## What does 100 percent specificity indicate?

### A low false positive rate

5

## What is the equation for positive predictive value?

### TP/(TP+FP)

6

## What is the positive predictive value?

### Probability that person actually has the disease given a positive test result

7

## What is negative predictive value?

### The probability that a person is actually drug free given a negative test result

8

## What is the equation of negative PPV?

### TN/(FN+TN)

9

## What is the true positive rate?

### Sensitivity

10

## What is the true negative rate?

### Specificity

11

## What is the equation for calculating incidence?

### Number of new cases/number of people in population at risk (don't already have the disease)

12

## What is the equation for prevalence?

### Number of cases in a population/total number of people in the population

13

## What is the equation for odds ratio?

###
Ad/bc

Used in case-control studies (outcome --> exposure)

14

## What is the equation for relative risk?

### A/(a+b)/c/(c+d)

15

## What is relative risk?

### Risk among exposed/risk among unexposed

16

## What is the equation for absolute risk?

###
(A/a+b) - (c/c+d)

(RR-1)/RR

#of adverse events in tx/# of adverse events in placebo

17

## What is the number needed to treat?

### The number of patients who need to be treated for 1 patient to benefit

18

## What is the equation for the number needed to treat?

###
1/absolute risk

1/ (event rate -control) - (event rate - tx)

19

## What is the number needed to harm?

### Number of patients who need to be exposed to a risk factor for 1 patient to be harmed

20

## What is the equation for the number needed to harm?

### 1/attributable risk = 1/(a/a+b) - (c/c+d)= 1/((RR-1)/RR)

21

## What is the equation for event rate?

### #of subjects per tx/total # of subjects

22

## What is precision?

### The consistency, reproduciblity and reliability of a test

23

## What lowers precision?

### Random error

24

## What is accuracy of a test?

###
Validity

Absence of systematic error

25

## What is the equation for SEM?

###
SD / square root sample size

So as sample size increases, standard error of mean decreases

26

## What is the null hypothesis?

###
Says there is no difference btween two groups

P = high

27

## What is the p-value?

###
The likelihood of observing what we did if the null is true.

The lower the p-value the more evidence for the alternative hypo

28

## What is a type I error?

###
False positive error

Stating there s a difference when there really isn't.

P-value is judged against this

Ex: convicting an innocent man

29

## What is a type II error?

###
Stating there isn't an effect or different when there is one

False negative error

Ex: Setting a guilty man free

30

## What is power?

###
The probablility of seeing a difference when one is there

Ex: convicting a guilty man

= 1- B

31

## What does power increase with?

###
Sample size

Expect effect size

Precision of measurement

32

## What is the equation for confidence interval?

###
Mean - Z(SEM) to mean + Z(SEM)

Z= 1.96 for 95% CI

Z = 2.58 for 99% CI

33