Topic 7: measure of association of odds ratio

Question 1

How to calculate the odds

Answer 1

Number of existing cases / number of non-cases

Question 2

Describe odds

Answer 2

• Measures likelihood of having outcome compared to not having outcome
• Instead of whole population only those non-diseased

Question 3

When is odds ratio used instead od relative risk?

Answer 3

• When it’s not possible to investigate prospectively with follow-ups
• Due to financial resources
• Limited time
• Outcome condition is very rare in population

Question 4

How is investigation done if cannot be done prospectively?

Answer 4

• Cross-sectionally = exposure + outcome assessed at same time
• Retrospectively = using existing outcome cases + go back in time to assess exposure
• Cannot calculate incidence + relative risk = use odds ratio

Question 5

How to calculate odds ratio

Answer 5

Odds in exposed / odds in unexposed

Question 6

How to interpret odds ratio

Answer 6

• > 1 = exposed have higher odds of outcome than unexposed = harmful
• <1 = exposed have lower odds of outcome than unexposed = protective
• =1= same odds as unexposed = no association