Measures of Association

Lecture given 9/4/2025

what does measures of disease association quantify?

the relationship between exposure and disease

what do relative differences tell us?

the relative increase or decrease in effect comparing one quantity to another

what do absolute differences tell us?

the absolute increase or decrease in effect

what is the equation for prevalence ratio?

prevalence exposed / prevalence unexposed

t/f prevalence ratio is commonly used in epidemiology

false

what is the equation for risk ratio?

risk exposed / risk unexposed

what is the range for risk ratio?

0 to + infinity

what are the units for risk ratio?

none

incidence rate ratio

ratio of incidence rates for two groups, the exposed versus unexposed

what is the equation for incidence rate ratio?

incidence rate exposed / incidence rate unexposed

what is the range of incidence rate ratio?

0 to + infinity

what are the units for incidence rate ratio?

none

what is the equation for odds ratio?

odds exposed / odds unexposed

what is the equation for risk difference?

risk exposed - risk unexposed

what is the range for risk difference?

-1 to 1

what are the units for risk difference?

none

what does risk measure?

the additional risk among those exposed when compared to those who are unexposed

what is the equation for incidence rate difference?

incidence rate exposed - incidence rate unexposed

what is the range for incidence rate difference?

-i nfinity to + infinity

what units does incidence rate difference have?

time

what does null mean?

there is no effect, or no association between the exposure and disease of interest

on the relative scale, null is equal to?

1

on the absolute scale, null is equal to?

0

what parameters are part of the relative scale?

prevalence ratio, risk ratio, incidence rate ratio, and odds ratio

what parameters are part of the absolute scale?

risk difference, incidence rate difference

what if the value is above null?

those who are exposed exhibit a higher (risk/rate/odds) of disease, compared to those who are unexposed

it is a positive association

what if the value is below null?

those who are exposed exhibit a lower (risk/rate/odds) of disease, compared to those who are unexposed

it is a negative association

risk difference provides?

a measure of the public health impact of the risk factor, and focuses on the number of cases that could potentially be prevented by eliminating the risk factor

dental caries

1.25, 5