Cross Sectional
Data from a group of people to assess frequency of dz at a particular point in time.
Asks "what is happening?
Case-control
Compares a group of people without a dz to a group with dz.
Asks "what happened?"
Retrospective
Patients with COPD had higher odds of a history of smoking than those without COPD.
Cohort
Compares a group with a given exposure or risk factor to a group without such exposure.
Looks to see if exposure increases likelihood of dz.
Prospective or retrospective
Asks "who will develop dz?" or "who developed the dz?"
Smokers had a higher risk of d
Twin concordance
Compares frequency with which both monozygotic twins or both dizygotic twins develop same dz.
Adoption study
Compares siblings raised by biological vs. adoptive parents.
Phase I of CT
Small number of healthy volunteers.
Safety
Toxicity
PCK
Pharmacodynamics
Phase II of CT
Small number of patients with dz of interest.
Treatment efficacy
Optimal dosing
Adverse effects
Phase III of CT
Large number of patients randomly assigned either to the treatment under investigation or to the best available treatment/placebo.
Compares new treatment to current standard of care.
Phase IV of CT
Postmarketing surveillance of patients after treatment is approved.
Rare or long-term adverse effects.
Selection bias
Error in assigning subjects to a study group resulting in an unrepresentative sample.
Recall bias
Awareness of disorder alters recall by subjects; common in retrospective studies.
Measurement bias
Information is gathered in a way that distorts it.
Procedure bias
Subjects in different groups are not treated the same.
Observer-expectancy bias
Researcher's belief in the efficacy of a treatment changes the outcome of that treatment.
Confounding bias
When a factor is related to both the exposure and the outcome, but not on the causal pathway; factor distorts or confuses effect of exposure on outcome.
Lead-time bias
Early detection time is confused with increased survival.
Mean
Most affected by outliers.
Median
If n=even number, the median will be the average of the middle two values.
Mode
Least affected by outliers.
Sample error of mean
SD
---
square root of n
SD distributions
1SD = 68%
2SD = 95%
3SD = 99.7%
Positive skew
Mean > median > mode
Long tail on
right
Negative skew
Mean < median < mode
Long tail on
left
Statistical hypotheses
Type I error
Stating there is an effect or difference when none exists.
Type II error
Stating there is not an effect or difference when one actually exists.
t-test
Checks difference between means of 2 groups.
ANOVA
Checks difference between means of
3 or more
groups.
Chi-square
Checks differences between 2 or more percentages or proportions of
categorical
outcomes.
Chi
tegorical outcomes.
Primary dz prevention
P
revent disease occurrence.
Secondary dz prevention
S
creening for early dz.
Tertiary dz prevention
T
reatment to reduce disability from dz.
Medicare is for (elderly/poor).
E
lderly
Medicaid is for (elderly/poor).
Poor =
D
estitute
Medicare part A
Hospit*A*l insur
A
A
pit*A*l insur*A*nce
Medicare part B
*B*asic medical
B
B
asic medical *B*ills
Medicare part C
Parts
A+B
delivered by approved private
C
ompanies
Medicare part D
Prescription
D
rugs