How can we compare different measures? Why should we compare them?
- by comparing their exposure status
- tells us if there is an association between exposure and disease
what is a noxious and beneficial exposure?
- noxious exposure is associated with having the disease
- Having beneficial exposure is associated with not having the disease
what are the two possible comparisons?
Index group (exposed)
Comparison/reference group (unexposed)
what are the two measures of comparison?
- Absolute measure: Calculating the difference between two measures of disease frequency
- Relative measure: Calculating the ratio of two measures of disease frequency
Why do we calculate absolute measures of comparison? relative measures?
- To represent the public health impact of the exposure on disease occurrence. (How much impact would prevention have? How many people have detrimental effects because of the harmful exposure?)
RR
- represent a measure of strength or magnitude of the association between an exposure and a disease.
- To help with etiologic research (identifying the cause of disease, benefits of treatments or therapies, etc.)( How much more likely are exposed persons to develop disease?)
How are P/CI/IR represented in absolute measures? general formula?
- prevalence - prevalence difference (PD)
- CI - risk difference (RD)
- IR- rate difference (IRD)
RD = Re-Ru
exposed - unexposed
what does RD=0,>,< mean?
- no association between E and D RD=0
- exposure is associated with an increased risk of disease then RD>0
- exposure is associated with decreased risk of disease then RD<0
what does RR=1,> or < 1?
- no association between exposure and disease RR=1
- Exposure is associated with an increased risk of Disease RR> 1
- Exposure is associated with a decrease risk of Disease RR<1
what does attributable mean?
used when casual association is assumed or known
what does attributable risk mean? what is this the same as?
-Excess rate or risk of disease among exposed population
- AR = RD - assuming a causal relationship
assuming a causal association between the exposure and health outcome APe is the same as? interpretation
- Attributable proportion among the exposed same as AR and AR%
- Excess proportion (percent) of disease among exposed population;
- assuming a causal relationship between E and D, the proprtion of disease in teh exposed group that can be attributed to exposure
- assuming a causal relationship between E and D, the proportion of disease among the exposed group that would have been prevented if teh exposure had not occured.
What is the name of APt that assumes a causal association between exposure and health outcomes? Interpretation?
- Population attributable risk percentage (PAR%)
- Excess proportion (percent) of disease in total population; if causal, the proportion of disease in total population that would be eliminated if the exposure was eliminated
- assuming a causal association between E and D,the excess proportion of D in the total population that can be attributed to the E
- assuming a causal association between E and D, the proportion of D in the total population that would have been prevented if exposure had not occurred
what is the name assuming a causal association of PRD? interpretation? helpful for?
- Population attributable risk/rate (PAR)
- PRD: population risk difference
- Excess rate or risk of disease in total population
- determining which exposure is the most important
what is the general formula for Relative risks?
RR= Re/Ru
what can RR stand for? and PR?
- risk ratio using CI data
- rate ratio or incidence density ratio using IR data
- prevalence ratio (PR) using prevalence data
what are the two generic formulas for calculating RR as a percentage?
- increase %: (RR-1) x 100 for RR>1 (excess or increase risk of disease)
- decrease %: (1-RR) x 100 RR<1 (reduced risk; protective effect)
How to interpret RR as a percentage?
The exposed are XX% more or less likely to develop the health outcome of interest than those who do not have the
exposure
what does a contingency table look like?
- where is E and D located? IV and DV?
- how to find R? and PT?
- exposed on the left and Diseased on the top
- ?
Re: a/a+b
Ru: c/c+d
Rt: a + c/ a+b+c+d
PTe = a
PTu= c
what is association?
- an identifiable relationship between exposure and disease
- comparison of risks or rates that yield an association
- implies exposure might cause disease
what are exposures associated with? observed associations don’t have to ?
- with differences in disease risks are called risk factors or preventative factors
- don’t have to represent a cause and effect
What are two ways to interpret an incidence rate ratio of 1.6?
The exposed group has 1.6 times the incidence rate of the unexposed group.
* The exposed group has a 60% excess/increased incidence rate as compared to the unexposed group.
o πππππππ‘ πβππππ πΌππππππ π (RR-1)x100 = (1.6-1)x100=60%
