# Measures of Association Flashcards

R = is defined as?

risk/prevalence

E+ = is defined as?

exposed positive

What does this equation tell you?

How many individuals out of the total have the disease?

E-

exposed negative

What does this equation tell you?

How many individuals out of the total do not have the disease?

Often reflects study population, not general population?

Example: Cohort study investigating feeding cats dry food (DF) and feline lower urinary tract disease (FLUTD). Based on the information in the table below, calculate the RE+, RE-, and Rtotal.

B/c we are looking at NEW cases of disease, it is incidence risk.

What is risk ratio (RR) also known as?

Relative Risk, Incidence Risk Ratio

How do you calculate the Risk Ratio (RR)?

Risk of exposed vs risk non-exposed

Calculate the RR for the FLUTD study we discussed above. Here are the values again:

4 x more risk for cats that ate the cat food versus those that did not eat the dry food. Can also be said “The risk of FLUTD is 4 times higher for cats on DF.”

How do you calculate Odds ratio?

What is the purpose of an odds ratio?

Odds: we are comparing in the exposed group looking at those that have the disease compared to those that do not have the disease, ALL int he exposed group.

What is this formula telling you?

The odds of disease in my exposed group divided by the odds of diseased in my non-exposed group.

Used in cohort and cross-sectional studies

It does not matter if we are looking at the odds of exposure in an exposed or diseased group. The difference is that some study designs start by first grabbing cases, sampling from population to grab controls. But in this scenario, when speaking about prevalence/risk makes no sense b/c you are dictating how many cases are in your study so you can not talk about risk in a case control study. You can speak about odds b/c in a case control study, we are interested in the odds of exposure in disease group and then look at healthy animals and look at odds of exposure in them. It does not matter which order you do it b/c you always get the same answer.

What is this formula telling you?

What are the odds of disease in my disease group divided by the odds of disease in my non-diseased group.

Used in case control-studies.

Example: Cohort study investigating feeding cats dry food (DF) and feline

lower urinary tract disease (FLUTD).

Calculate the OE+, OE-, and OR.

What is the effect in this case?

No effect

Risk and/or odds of disease are the same.

When there is no difference between exposed and non-exposed, you will get a 1.