biostats = lame Flashcards
Design:
Collect data from a group of people to assess the freqency of disease (and related risk factors) at a particular point in time.
Ask what is happening?
Study type?
Cross-sectional Study
- observation
- measure the disease prevalence
- can show risk factor association
YOU CANNOT establish causality
Design: Compare a group of people with disease to a group without the disease. Looks for a prior exposure or risk factor, asks what happenED?
Case-Control
-observation, prospective or retrospective
You calculated an odds ration
“Patients with COPD had higher odds of history of smoking than those without COPD”
Design:
Compares a group with a give exposure or risk factor to a group without such exposure. Looks to see if exposure increases the likelihood of disease. Can be prospective asks who will develop the disease? or retrospective, who developed the disease the exposed vs non exposed?
Cohort study
-calculate relative risk RR
“smokes had a higher risk of developing COPD than nonsmokers”
Design: Compares frequency with which both monozygotic twins or both dizygotic twins develop same disease
Twin concordence study
-measure heritability and influence of environmental factors
Design: Compares siblings raised by biological vs. adoptive parents
Adoption study
Measures heritability and influence of environmental factors
How to improve study quality in random trials
randomized, controlled and double blinded. Triple blind refers to the additional blinding of the researchers analyzing the data
Drug trial phases
Phase 1: small number of healthy volunteers
is it safe?
Phase II: Small number of patients with the disease
Does it work?
Phase III: Large number of patients randomly assigned either to the treatment under investigation or to the best available treatment (or placebo)
Is it good or better?
Phase IV: postmarketing surveillace trial of patients after approval, Can it stay? Detects rare or long-term adverse effects. Can result in a drug being withdrawn
Incidence
looks at new cases, incidents
Incidence rate = # of new cases in a specified time period/population at risk during same time period
Prevalence
Prevalence looks at all current cases # of existing cases/population at risk
prevalence roughly equal to the incidence rate X average disease duration
- incidence and prevalence for common short duration diseases are similar like the cold
- the prevalence > incidence for a chronic disease like DM
How to make a 2x2 square for quantifying risk
top disease + or - side we have risk factor + or _ \+- \+ab -cd
Odds ratio - typically used for
Case-control
odds that the group with the disease (cases) was exposed to a risk factor a/c divided by the odds that the group without the disease (controls) was exposed b/d
a/c /b/d = ad/bc
Relative risk typically used for
cohort studies
Risk of developing disease in the exposed group divided by the risk in the unexposed group 21% of smokers develop lung cancer vs 1 % of non smokers 21/1
if prevalence is low RR roughly = OR
rr= a/a+b /c/c+d
relative risk reduction RRR
the proportion of risk reduction attributable to the intervention as compared to a control.
RRR = 1-RR
ex if 2% of patients who recieve the flu shot (risk) got the flu and 8% of patients who did not get the flu shot got the flu (no shot risk) then rr = 2/4 = 0.25
RRR = 1-0.25 = 0.75
Atributable risk
the difference in risk between the exposed and the unexposed groups, or proportion of disease occurrences that are attributable tot he exposures.
AR = a/a+b - C/C+D
so if 21% risk of lung cancer in smokers and a 1% risk in non smokers than the AR = 21-1 = 20%
