Biostats

Question 1

a test is negative, what is the chance that you really dont have the disease?

Answer 1

NPV

Question 2

what is “matching” and what bias does it decrease

Answer 2

“matching’ is pairing subects of similar age/SS.. ex: CRC patients and their neighbors of similar race w/o CRC
the goal is to decrease confounding bias

Question 3

what is the Hawthorne Effect?

Answer 3

Subject changes behavior once they know they are being watched

Question 4

How do you predict the risk in a person with X behavior? Attributable Risk in Exposed?

Answer 4

ARP= 100* ( RR-1/ RR)

Question 5

what study method SIMULTANEOUSLY measures exposures and outcomes

Answer 5

Cross Sectional Study- “a snapshot”

Question 6

the probability of concluding there is no difference when one exists, is what?

Answer 6

Beta error

Question 7

what is the power of a study

Answer 7

1-B

Question 8

the probability of concluding there is a difference when there isn’t one (just chance)

Answer 8

alpha error

Question 9

the patient tests positive, what are the chances that the patient has disease X?

Answer 9

PPV= TP/ TP+FP

Question 10

what is resistant to outliers?

Answer 10

MODE

Question 11

incidence v prevelance

Answer 11

new cases/pop@risk vs total cases/total pop

Question 12

what is relative risk?

Answer 12

(the risk w/ drug X of getting disease Y)/ (the risk w/o X of getting Y)

Question 13

T/F assistive walking devices show reduced risk of falls

Answer 13

FALSE- they do increase mobility. but need medication review in elderly to decrease falls

Question 14

stratification decreases risk of what bias?

Answer 14

confounding

Question 15

case control studies use WHAT stat measurement

Answer 15

Odds ratio

Question 16

what is attrition bias?

Answer 16

loss of patients to follow-up from a specific group, can skew results, is a form of selection bias

Question 17

screening tests should have a high___ and confirmatory tests should have a high ____

Answer 17

(1) sensitivity

(2) specificity

Question 18

Number Needed to harm when comparing two treatments

Answer 18

1/ (absolute risk increase)
so step 1: calculate the risk of harm in drug X, and then drug Y
step 2: subtract the risk of harm in X from Y = absolute risk increase
step 3: do the inverse fraction of that= 1/ARI

Question 19

how do you choose the 2 groups in a case control study?

Answer 19

(1) pts that HAVE the disease

2) pts that dont HAVE the disease (and have NORMAL exposure risks

Question 20

case fatality rate=

Answer 20

(# of fatal cases of X)/ (# of fatal and nonfatal cases of X)

Question 21

more sensitive screening tests can detect disease EARLIER and while the prognosis is actually unchanged, there is an “apparent increase” in survival time .. what is this bias?

Answer 21

Lead time bias

Question 22

confused about if something is statistically significant? what should you check?

Answer 22

Confidency interval!

If it crosses the NULL, than it is not statistically significant

Question 23

who is eligible for MediCARE

Answer 23

elderly >65

disabled: ALS, ESRD, Cerebral Palsy

Question 24

in either a positive or a negative skewed bell graph curve what variables are the most skewed to the least skewed

Answer 24

Mean» median»mode

Question 25

if you are trying to compare the means of 3+ groups what test would you use?

Answer 25

ANOVA

analysis of variance

Question 26

a “snapshot” of “POPULATION” data and prevelance/incidence of X disease in a POPULATION is what kind of study?

Answer 26

Ecological Study

note cross-sectional is also a “snapshot” like this but used for individual’s data

Question 27

if you stratify something and there IS a significant difference in the strata, it is ___
and if there isn’t a significant difference in the strata

Answer 27

effect modification

confounding bias

Question 28

how to determine correlation coefficient

Answer 28

(1) is it positive or negative ( direct or inverse relationship, respectively)
(2) are the plot points kind of close together/looking linear-ish (then it is closer to -1 or 1)
if the plot points are more scattered, it is farther from -1 or 1, more like 0.2 or -0.2

Question 29

whats the SD rule?

Answer 29

68/95/99.7

Question 30

how do you decide how many people to treat before one person is cured?

Answer 30

1/ ARR

ARR= control event rate- experimental event rate

Question 31

how to compare two categorical variables

Answer 31

Chisquare test

Question 32

how do you do an Odd’s ratio for the occurence of X with drug Y

Answer 32

(((X w/ drug)/ (X without drug))) / (((no X with drug)/ (no X without drug)))