Odds Ratio: Definition, Calculation, Interpretation.

1. Odds Ratio
Basic Concepts

2.  Definition
 Calculation
 Interpretation

3. ODDS Ratio
ODDS
RATIO
Ratio: Is the number (a) of observations in a given
group with a given characteristic ( such as having
an MI) divided by the number (b) of observations
without the given characteristic (such as not having
MI).
‫تناسب‬

4. ODDS Ratio
ODDS
RATIO
ODDS: The probability that an event will
occur divided by the probability that the
event will not occur.
‫تحيز‬ ، ‫رجحان‬

5. • Definition:
Is the ODDS that a patient is exposed to
the risk factor divided by the ODDS that a
control is exposed

6. Table.: Data for odds ratio for stroke
with history of drug abuse

7. Calculation

8. STEP One: Calculate the odds that a patient
( With stroke) is exposed ( Abused drugs ) :
1
1
2
2
Exposed
Not Exposed
Cases
The probability that an event will occur
The probability that the event will not occur.

9. STEP Two: Calculate the odds that a control
( Without stroke) is exposed ( Abused drugs ) :
1
1
2
2
The probability that an event will occur
The probability that the event will not occur.

10. STEP Three
ODD
ODD

11. Interpretation
the odds is 5.64
That is, a person in this study who
abuses drugs is more than five times
more likely to have a stroke

12. An odds ratio of

13. SO,,
• An odds ratio is measure of association which
quantifies the relationship between an
exposure and health outcome from a
comparative study.
• This feature is particularly relevant when we
analyze data from a case-control study, which
has a group of cases and a group of non-cases
or controls.