Biostatistics Flashcards
case control study
observational and retrospective comparison of people with a disease to people without
trying to find a risk factor
odds ratio
cohort study
observational and retro/prospective comparison of group with exposure/risk factor to a group without risk factor
see if exposure increases likelihood
relative risk
cross-sectional study
observational collection of data from a group to assess frequency at one time
cannot demonstrate causality
finds disease prevalence
twin concordance
measures heritability
adoption study
measures heritability vs environment
clinical trial phases
I: is drug safe on healthy individuals
II: does drug work in sick pts
III: does drug work better
IV: postmarketing surveillance
sensitivity
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
specificity
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)
positive predictive value
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
negative predictive value
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
incidence
new cases of a disease
=# new cases/population at risk
prevalence
looks at all current cases
=# existing cases/population at risk
~incidence rate*duration of disease
prevalence>incidence for chronic diseases
odds ratio
case control studies.
=odds of exposure in disease group/odds of exposure in healthy group
=(a/b)/(c/d)
relative risk
cohort
=risk of developing disease when exposed/risk in unexposed group
=[a/(a+b)]/[c/(c+d)]
if prevalence is low RR ~ OR
attributable risk
proportion of disease attributable to exposure
=a/(a+b)-c/(c+d)
=incidence exposed-incidence unexposed
absolute risk reduction
reduction in risk associated with a treatment as compared to a control
number needed to treat
# treated for 1 person to benefit =1/absolute risk reduction
number needed to harm
# patients exposed to risk factor before 1 patient is harmed =a/attributable risk
precision
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
accuracy
trueness of a test measurement (validity)
systematic error reduces accuracy
confounding bias
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
Pygmalion effect
when a researcher’s belief in efficacy changes the outcom
AKA observer-expectancy effect
Hawthorne effect
when behavior changes because person is being studied
positive skew
mean>median>mode
longer tail on right
negative skew
mean<mode
longer tail on left
SEM (standard error of mean)
=SD/sqrt(n)
SEM decreases as n increases
type I error
alpha error
states there is a difference when none exists
mistakenly rejects the null hypothesis (p>0.05)
false-positive error
type II error
beta error
there is not a difference when one exists
fail to reject the null when it is false
false-negative error
Power
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
confidence interval
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
standard deviations
1=68%
2=95%
3=99.7%
primary prevention
prevent disease from occuring
vaccines or condoms
secondary prevention
early detection of disease
PAP smear or other screening tests
tertiary prevention
reduce disability from disease
chemotherapy for cancer
car seats
4: until weight/height limit of seat is reached, then do booster until they are 4’9” and 8-12 years of age
important preventive measures in high-risk sexual behavior
chlamydia and gonorrhea screen (women) HIV screen Syphilis screen (MSM, trade sex for money) Hep B vaccine Pap smear HPV screen and vaccine
Kubler-Ross grief stages
denial anger bargaining grieving (depression) acceptance can be in any order or skipped
Beneficence
act in patient’s best interest
autonomy
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)
nonmaleficience
do no harm
balance benefits with risk
justice
treat patients fairly
do not treat pts differently from one another
4 elements of malpractice
duty (physician treated you)
breach of duty
harm
damage
