odds ratios (basic concepts)
TRANSCRIPT
Odds Ratio
Odds RatioBasic Concepts
Odds Ratio
Dr. Alazabee Tarek
Group Discussion
ODDS RATIO
Definition
Calculation
Interpretation
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).
RATIO = A / B
تناسب
ODDS
Ratio
ODDS RATIO
ODDS: The probability that an event will occur divided by the probability that the event will not occur.
ODDS = P / (1-P)
، رجحانتحيز
Odds Ratio ( OR )
• Definition: Is the ODDS that a patient is exposed to
the risk factor divided by the ODDS that a control is exposed
Case Control Study
Table.: Data for odds ratio for stroke with history of drug abuse
Stroke Control
Drug Abuse 73 18
No Drug Abuse 141 196
Total 214 214
Calculation
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.
STEP Two: Calculate the odds that a control ( Without stroke) is exposed ( Abused drugs ) :
1
1
2
2
Exposed
Not Exposed
The probability that an event will occur
The probability that the event will not occur.
STEP Three
ODD
ODD
Interpretationthe 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
An odds ratio of
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.