Biostatistics

Question 1

case control study

Answer 1

observational and retrospective comparison of people with a disease to people without
trying to find a risk factor
odds ratio

Question 2

cohort study

Answer 2

observational and retro/prospective comparison of group with exposure/risk factor to a group without risk factor
see if exposure increases likelihood
relative risk

Question 3

cross-sectional study

Answer 3

observational collection of data from a group to assess frequency at one time
cannot demonstrate causality
finds disease prevalence

Question 4

twin concordance

Answer 4

measures heritability

Question 5

adoption study

Answer 5

measures heritability vs environment

Question 6

clinical trial phases

Answer 6

I: is drug safe on healthy individuals
II: does drug work in sick pts
III: does drug work better
IV: postmarketing surveillance

Question 7

sensitivity

Answer 7

proportion of people with disease who test positive, probability test detects disease when present
SNOUT: sensitivity rules OUT
TP/(TP+FN) = a/(a+c) = 1-FN rate

Question 8

specificity

Answer 8

proportion without disease who test negative, probability a test indicates non-disease when disease is absent
SPIN: specificity rules IN
TN/(TN+FP) = d/(d+b)

Question 9

positive predictive value

Answer 9

proportion of positive results that are true positives, probability has disease when test is positive
=TP/(TP+FP) = a/(a+b)
varies directly with prevalence

Question 10

negative predictive value

Answer 10

negative test results that are true negatives, probability person is disease free when test is negative
=TN/(FN+TN) = d/(d+c)
varies inversely with prevalence

Question 11

incidence

Answer 11

new cases of a disease

=# new cases/population at risk

Question 12

prevalence

Answer 12

looks at all current cases
=# existing cases/population at risk
~incidence rate*duration of disease
prevalence>incidence for chronic diseases

Question 13

odds ratio

Answer 13

case control studies.
=odds of exposure in disease group/odds of exposure in healthy group
=(a/b)/(c/d)

Question 14

relative risk

Answer 14

cohort
=risk of developing disease when exposed/risk in unexposed group
=[a/(a+b)]/[c/(c+d)]
if prevalence is low RR ~ OR

Question 15

attributable risk

Answer 15

proportion of disease attributable to exposure
=a/(a+b)-c/(c+d)
=incidence exposed-incidence unexposed

Question 16

absolute risk reduction

Answer 16

reduction in risk associated with a treatment as compared to a control

Question 17

number needed to treat

Answer 17

# treated for 1 person to benefit
=1/absolute risk reduction

Question 18

number needed to harm

Answer 18

# patients exposed to risk factor before 1 patient is harmed
=a/attributable risk

Question 19

precision

Answer 19

reliability of values=reproducible findings
does not mean the values are correct, just close to being the same
random error reduces precision in a test

Question 20

accuracy

Answer 20

trueness of a test measurement (validity)

systematic error reduces accuracy

Question 21

confounding bias

Answer 21

when a third variable that affects the outcome and exposure is not taken into account
Ex: coffee drinkers are more likely to get cancer because smokers are more likely to drink coffee. Smoking increases cancer, not coffee

Question 22

Pygmalion effect

Answer 22

when a researcher’s belief in efficacy changes the outcom

AKA observer-expectancy effect

Question 23

Hawthorne effect

Answer 23

when behavior changes because person is being studied

Question 24

positive skew

Answer 24

mean>median>mode

longer tail on right

Question 25

negative skew

Answer 25

mean<mode

longer tail on left

Question 26

SEM (standard error of mean)

Answer 26

=SD/sqrt(n)

SEM decreases as n increases

Question 27

type I error

Answer 27

alpha error
states there is a difference when none exists
mistakenly rejects the null hypothesis (p>0.05)
false-positive error

Question 28

type II error

Answer 28

beta error
there is not a difference when one exists
fail to reject the null when it is false
false-negative error

Question 29

Power

Answer 29

1-B error
probability of rejecting null hypothesis when it is false
likelihood of finding a difference if one exists
increases with: sample size, precision of measurement, increased expected effect

Question 30

confidence interval

Answer 30

range [mean-ZSEM]-[mean+ZSEM]
Z is a factor for confidence interval
for 95% CI Z=1.96
for 99% CI Z=2.58
for 90% CI Z=1.645
if CI crosses 0, then you cannot reject Ho (there is no difference in groups)
if CI includes 1 for odds ratio or relative risk, you cannot reject Ho

Question 31

standard deviations

Answer 31

1=68%
2=95%
3=99.7%

Question 32

primary prevention

Answer 32

prevent disease from occuring

vaccines or condoms

Question 33

secondary prevention

Answer 33

early detection of disease

PAP smear or other screening tests

Question 34

tertiary prevention

Answer 34

reduce disability from disease

chemotherapy for cancer

Question 35

car seats

Answer 35

4: until weight/height limit of seat is reached, then do booster until they are 4’9” and 8-12 years of age

Question 36

important preventive measures in high-risk sexual behavior

Answer 36

chlamydia and gonorrhea screen (women)
HIV screen
Syphilis screen (MSM, trade sex for money)
Hep B vaccine
Pap smear
HPV screen and vaccine

Question 37

Kubler-Ross grief stages

Answer 37

denial
anger
bargaining
grieving (depression)
acceptance
can be in any order or skipped

Question 38

Beneficence

Answer 38

act in patient’s best interest

Question 39

autonomy

Answer 39

Pt: has the right to know their options and choose what happens
doctor: must respect the Pt’s decision, but have the right to deny services if it is against their beliefs (prescribing birth control if you are religious, but you should refer to another physician)

Question 40

nonmaleficience

Answer 40

do no harm

balance benefits with risk

Question 41

justice

Answer 41

treat patients fairly

do not treat pts differently from one another

Question 42

4 elements of malpractice

Answer 42

duty (physician treated you)
breach of duty
harm
damage