Biostats

Question 1

sensitivity

Answer 1

TP / TP+FN

A / A+C

Question 2

specificity

Answer 2

TN / TN+FP

D / B+D

Question 3

positive predictive value

Answer 3

TP / TP+FP

A / A+B

Question 4

negative predictive value

Answer 4

TN / TN+FN

D / C+D

Question 5

what is the relationship between NPV and pretest probability?

Answer 5

inverse

Question 6

case-control compares:

Answer 6

risk factor frequency

patients selected based on if they have the disease or not

looks backwards to see if they had past exposure to a risk factor

Question 7

odds ratio

Answer 7

used in case-control

(A/C) / (B/D) = (case;exposed) / (control;not exposed)

(A x D) / (B x C)

Question 8

cohort study compares:

Answer 8

disease incidence

both groups start with the disease; patients selected based on exposure

looks forward or backward at various factors over time

Question 9

relative risk

Answer 9

used in cohort

(A / A+B) / (C / C+D)

(risk;exposed) / (risk;not exposed)

Question 10

cross-sectional study compares:

Answer 10

disease prevalence

Question 11

prevalence

Answer 11

disease burden in a population at any given time

Question 12

incidence

Answer 12

number of new cases in a population in a given time

Question 13

power

Answer 13

1 - beta (FN)

power is related to sample size

Question 14

false negative

Answer 14

type II error

beta error

Question 15

false positive

Answer 15

type I error

alpha error

Question 16

standard deviations

Answer 16

1 SD = 68%

2 SD = 95%

3 SD = 99.7%

Question 17

normal distribution

Answer 17

mean = median = mode

Question 18

postively (right) skewed distribution

Answer 18

mean > median > mode

Question 19

negatively (left) skewed distribution

Answer 19

mean < median < mode

Question 20

case-fatality rate

Answer 20

fatal cases / total case occurences

Question 21

risk

Answer 21

rate of an adverse event

affected / total

Question 22

absolute risk reduction

Answer 22

control risk — treatment risk

(affected/total;control) — (affected/total;treatment)

Question 23

relative risk reduction

Answer 23

ARR / control rate

[control risk — treatment risk] / control risk

[(affected/total;control) — (affected/total;treatment)] / (affected/total;control)

Question 24

absolute risk increase

Answer 24

treatment risk — control risk

(affected/total;treatment) — (affected/total;control)

Question 25

number needed to harm

Answer 25

1 / absolute risk increase

1 / [treatment risk — control risk]

1 / [(affected/total;treatment) — (affected/total;control)]

Question 26

number needed to treat

Answer 26

1 / absolute risk reduction

1 / [control risk — treatment risk]

1 / [(affected/total;control) — (affected/total;treatment)]

the samller the NNT, the better

Question 27

positive likelihood ratio

Answer 27

sensitivity / (1 - specificity)

[TP / (TP + FN)] / [1 — (TN / (TN + FP)]

Question 28

negative liklihood ratio

Answer 28

(1 - sensitivity) / specificity

[1 — (TP / (TP + FN)] / (TN / (TN + FP)

Question 29

confidence interval

Answer 29

the null is 1.0

if it includes the null (1.0) it is not statistically significant

Question 30

attributable risk perentage

Answer 30

percentage of disease in an exposed group that can be attributed to the exposure

[(risk;treatment) — (risk;control)] / (risk;treatment)

(relative risk — 1) / relative risk

Question 31

IV qualitative X DV qualitative

Answer 31

Chi square

Question 32

IV quantitative X DV qualitative

Answer 32

logisitc regression

Question 33

IV quantitative X DV quantitative

Answer 33

linear regression

Question 34

IV qualitative x DV quantitative

Answer 34

t-test, ANOVA