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