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