Biostatistics

Question 1

attack rate =

Answer 1

number of individuals who become ill divided by the number of individuals who are at risk of contracting that illness

Question 2

the ______ of test refers to its ability to correctly ID those with the disease. A highly ______ test should be chosen over a highly ______ test when screening for life threatening diseases

Answer 2

sensitivity

sensitive

specific

Question 3

1 SD away from the mean =

2 SD away from the mean =

3 SD away from the mean =

Answer 3

68% (16 on each side of the curve)

95% (2.5 on each side of the curve)

99.7% (.15 on each side of the curve)

Question 4

If the CI crosses the null value = 0, then there is

Answer 4

no statistical significance

Question 5

in a _________ subjects are randomly allocated to a sequence of 2 or more treatments given consecutively. A washout period is often added between treatment intervals to limit the confounding effects of prior treatment

Answer 5

Cross over study

Question 6

_______ is present when the effect of the main exposure on the outcome is modified by the presence of another variable

Answer 6

effect modification

Question 7

the _________ of a test refers to its ability to correctly ID individuals without the disease

Answer 7

specificity

Question 8

the mean is the ______

the mode is the ______

the range is the _____

an outlier will not effect the ____

Answer 8

average

most frequent

difference from largest to smallest

mode

Question 9

PPV =

Answer 9

TP/(TP+FP)

Question 10

incidence corresponds to the ________ of a disease in a certain population at risk over a given period of time. _______ is the total number of cases in the population over a given period of time

Answer 10

number of new cases

prevalence

Question 11

True negatives =

false positives =

specificity =

sensitivity =

Answer 11

specificity x number of patients confirmed without the disease

1 - specificity x the number of patients confirmed without he disease

d/(b+d)

a/(a+c)

Question 12

the cutoff value of a quantitative diagnostic test determines whether a given result is interpreted as positive or negative. Lowering the cutoff point typically causes ________, which decreases the false negative number and increases the sensitivity and decreases the specificity. =

Answer 12

more patients with the disease to test positive

Question 13

cases and controls should be selected based on _________, not exposure status

Answer 13

disease status

Question 14

prompt treatment of grpA strep pharyngitis could reduce the incidence of

Answer 14

ARF

Question 15

matching is used in case controls studies in order to control ___________

Answer 15

confounding variables

Question 16

the mean measure of association in a case control study used to compare exposure status of people with disease vs people without disease is the ______

Answer 16

odds ratio

Question 17

the _______ or observer effect is the tendency of study subjects to change their behavior as a result of their awareness that they’re being studied

Answer 17

Hawthorne effect

Question 18

ARR =

Answer 18

event rate in the control group - event rate in the treatment group

Question 19

statistical ______ = (1-Beta) is the probability of rejecting the null hypothesis when it is truly false. It is typically set at 80% and depends on sample size and difference between outcomes

Answer 19

power

Question 20

allele frequency =

phenotypic frequency

mutant allele frequency from disease prevalence

Answer 20

p + q = q

p^2 + 2pq + q^2 = 1

square root(q^2) = q

Question 21

The odds ratio is =

Answer 21

ad/bc

Question 22

exposure to a risk factor or risk reducing factor sometimes occurs years before clinical manifestations of a disease are evident. THis is called

Answer 22

latent period

Question 23

if the 95% CI does not cross the null value, the p value must be

Answer 23

<0.05

Question 24

if events are independent (blood samples) the probability that all events will turn out the same is the ________ of the separate probabilities for each event

Answer 24

product

Question 25

in a _________ exposure and outcome are measured simultaneously at a particular point in time (snapshot)

Answer 25

cross sectional

Question 26

________ values are influenced by disease prevalence in a target population while sensitivity, specificity, and likelihood ratios are not prevalence dependent

Answer 26

positive and negative predictive values

Question 27

CI of mean =

Answer 27

Mean + or - 1.96(SDsquareroot(n))

Question 28

Number needed to harm =

ARR =

Answer 28

1/ARR

adverse event rate in experimental group - adverse event rate in control group

Question 29

relative risk reduction = (absolute risk - absolute risk treatment)/ARcontrol

or Standard recurrence rate - [desired recurrence rate reduction x (_________)]

Answer 29

standard recurrence rate

Question 30

______ occurs when new test diagnoses a condition earlier than conventional studies, causing an apparent increase in survival time

Answer 30

lead time bias

Question 31

a _____ is used to compare the difference between the means of 2 groups. ____ compares the difference between the means of 2 or more groups.

Answer 31

T test

ANOVA

Question 32

____ is the probability of developing a disease over a certain period of time. To calculate this probability, divide the number of affected subjects by the total number of subjects in the corresponding exposure group

Answer 32

Risk

Question 33

the _______ represent the risk of an outcome in the exposed divided by the risk of that outcome in the unexposed. this is equal to [a/(a+b)]/[c/(c+d)]

Answer 33

Relative risk

Question 34

the unit of analysis in ______ is populations not individuals

Answer 34

ecological studies

Question 35

______ results from study participants inaccurate recall of past exposure and occurs most often in retrospective studies

Answer 35

recall bias

Question 36

a studies power increases as its _______. therefore the larger the sample, the greater the ability of a study to detect a difference when one truly exists

Answer 36

sample size increases

Question 37

the attributable risk percent in the exposed represents the excess risk in the exposed population that can be attributed to the risk factor (smoking). It can be derived by ARPexposed =

Answer 37

100x [(RR-1)/RR]

Question 38

________ is calculated by dividing the number of fatal cases of a disease by the total number of people with that disease or condition

Answer 38

case fatality rate

Question 39

in prospective studies, disproportionate loss to follow up between the exposed and unexposed groups creates the potential for attrition bias, which is a form of

Answer 39

selection bias

Question 40

a factor that prolongs disease duration (improved quality of care) will ________________

Answer 40

increase disease prevalence