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Flashcards in Biostats Deck (32)
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1
Q

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

A

NPV

2
Q

what is “matching” and what bias does it decrease

A

“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

3
Q

what is the Hawthorne Effect?

A

Subject changes behavior once they know they are being watched

4
Q

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

A

ARP= 100* ( RR-1/ RR)

5
Q

what study method SIMULTANEOUSLY measures exposures and outcomes

A

Cross Sectional Study- “a snapshot”

6
Q

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

A

Beta error

7
Q

what is the power of a study

A

1-B

8
Q

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

A

alpha error

9
Q

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

A

PPV= TP/ TP+FP

10
Q

what is resistant to outliers?

A

MODE

11
Q

incidence v prevelance

A

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

12
Q

what is relative risk?

A

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

13
Q

T/F assistive walking devices show reduced risk of falls

A

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

14
Q

stratification decreases risk of what bias?

A

confounding

15
Q

case control studies use WHAT stat measurement

A

Odds ratio

16
Q

what is attrition bias?

A

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

17
Q

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

A

(1) sensitivity

(2) specificity

18
Q

Number Needed to harm when comparing two treatments

A

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

19
Q

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

A

(1) pts that HAVE the disease

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

20
Q

case fatality rate=

A

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

21
Q

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?

A

Lead time bias

22
Q

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

A

Confidency interval!

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

23
Q

who is eligible for MediCARE

A

elderly >65

disabled: ALS, ESRD, Cerebral Palsy

24
Q

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

A

Mean» median»mode

25
Q

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

A

ANOVA

analysis of variance

26
Q

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

A

Ecological Study

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

27
Q

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

A

effect modification

confounding bias

28
Q

how to determine correlation coefficient

A

(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

29
Q

whats the SD rule?

A

68/95/99.7

30
Q

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

A

1/ ARR

ARR= control event rate- experimental event rate

31
Q

how to compare two categorical variables

A

Chisquare test

32
Q

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

A

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