Biostats

Question 0

What does 100% sensitivity indicate?

Answer 0

Low false negative rate

Question 1

What is the equation for sensitivity?

Answer 1

TP/(TP+FN)

Question 2

What is sensitivity used for?

Answer 2

Used for screening in diseases with low prevalence

Question 3

What is the equation for specificity?

Answer 3

TN/(TN+FP)

Question 4

What does 100 percent specificity indicate?

Answer 4

A low false positive rate

Question 5

What is the equation for positive predictive value?

Answer 5

TP/(TP+FP)

Question 6

What is the positive predictive value?

Answer 6

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

Question 7

What is negative predictive value?

Answer 7

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

Question 8

What is the equation of negative PPV?

Answer 8

TN/(FN+TN)

Question 9

What is the true positive rate?

Answer 9

Sensitivity

Question 10

What is the true negative rate?

Answer 10

Specificity

Question 11

What is the equation for calculating incidence?

Answer 11

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

Question 12

What is the equation for prevalence?

Answer 12

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

Question 13

What is the equation for odds ratio?

Answer 13

Ad/bc

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

Question 14

What is the equation for relative risk?

Answer 14

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

Question 15

What is relative risk?

Answer 15

Risk among exposed/risk among unexposed

Question 16

What is the equation for absolute risk?

Answer 16

(A/a+b) - (c/c+d)
(RR-1)/RR
#of adverse events in tx/# of adverse events in placebo

Question 17

What is the number needed to treat?

Answer 17

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

Question 18

What is the equation for the number needed to treat?

Answer 18

1/absolute risk

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

Question 19

What is the number needed to harm?

Answer 19

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

Question 20

What is the equation for the number needed to harm?

Answer 20

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

Question 21

What is the equation for event rate?

Answer 21

of subjects per tx/total # of subjects

Question 22

What is precision?

Answer 22

The consistency, reproduciblity and reliability of a test

Question 23

What lowers precision?

Answer 23

Random error

Question 24

What is accuracy of a test?

Answer 24

Validity

Absence of systematic error

Question 25

What is the equation for SEM?

Answer 25

SD / square root sample size

So as sample size increases, standard error of mean decreases

Question 26

What is the null hypothesis?

Answer 26

Says there is no difference btween two groups

P = high

Question 27

What is the p-value?

Answer 27

The likelihood of observing what we did if the null is true.
The lower the p-value the more evidence for the alternative hypo

Question 28

What is a type I error?

Answer 28

False positive error
Stating there s a difference when there really isn’t.
P-value is judged against this
Ex: convicting an innocent man

Question 29

What is a type II error?

Answer 29

Stating there isn’t an effect or different when there is one
False negative error
Ex: Setting a guilty man free

Question 30

What is power?

Answer 30

The probablility of seeing a difference when one is there
Ex: convicting a guilty man
= 1- B

Question 31

What does power increase with?

Answer 31

Sample size
Expect effect size
Precision of measurement

Question 32

What is the equation for confidence interval?

Answer 32

Mean - Z(SEM) to mean + Z(SEM)
Z= 1.96 for 95% CI
Z = 2.58 for 99% CI

Question 33

What is the equation for likelihood ratio?

Answer 33

Sensitivity/1-specifity

The higher the better likelihood the patient has a disease they are being treated for