Quantifyng Risk Flashcards
epidimiology - OR RR
Odds ratio Relative risk
epidimiology - RRR AR
Relative risk reduction Attributable risk
epidimiology - ARR
Absolute risk reduction
Odds ratio used in
Case control studies
Odds ratio
Odds that the group with the disease (cases) was exposed to a risk factor divided by odds that the group without disease (controls) was exposed
Relative risk typically used in
Cohort studies
Odds ratio equation (and explanation)
OR=(a/c)/(b/d)=ad/bc = X
the risk of the disease is X times higher for exposed then non exposed in population
Relative risk
Risk of developing disease in the exposed group divided by risk in the unexposed group
epidemiology - RR equation
(a/(a+b))/(c/(c+b))
if prevelance is low –> RR? OR?
RR=OR
Relative risk reduction (RRR)
The proportion risk reduction attributable to the intervention as compared to a control
(how much the risk is reduced by the intervention)
Attributable risk (AR)
The difference in risk between exposed and unexposed groups
or,
The proportion of disease that are ATTRIBUTABLE to the exposure
Relative risk reduction example
2% of patients who receive a flu shot develop flu
8% of unvaccinated patients develop the flu
RR=0,25
RRR=1-RR=1-0,25=0,75.
Or RRR=(8-2)/8 = 6/8 = 0.75
Absolute risk reduction
The difference risk (not the proportion) attributable to the intervention as compared to control)
Attributable risk (AR) equation
AR=a/(a+b)-c/(c+d)
Number needed to treat (NNT)
Number of patients who need to be to be treated for 1 patient to benefit
Absolute risk reduction example
8% placebo flu - 2% vaccine flu = 6% = 0,6
Number needed to treat calculation
1/ARR
Number needed to harm
Number of patients who need to ge exposed to a risk factor for 1 patient to be harmed
Number needed to harm calculation
1/AR
Attributable risk example
If risk for lung cancer is 21% in smokers and 1 in nonsmokers, then 20% of the lung cancer risk in smokers is attributed to smoking
Relative risk example
21% smokers develop lung ca and 1% of non smoker
RR=21/1 = 21
of 200 patients, 50 have lung Ca. Of these, 45 are smokers. Of remaining 150 patients (no Ca) ,60 are smokers –> Odds Ratio
(45/5)/(60/90) = (45x90)/(5x60) = 13.5
The risk of Lung Ca is 13.5 times higher for smokers than in nonsmokers in this population
Quantifyng Risk - TABLE
DISEASE
+ -
RISK FATCTOS + a b
(or intervention) - c d
