Odds Ratio

rasheed · Oct 22, 2009

The formula for odds ratio is easily remembered

The years can either be AD or BC
AD = Anno Domini, After christ
BC = Before Christ

The odds ratio
OD = AD/BC

Of course remember that the A cell is always the disease with the risk and then simply cross to the D cell and divide by the other two cells.

So for example in this 2X2 table
The AD cells are in red and the BC cells are in yellow
The A cell is the number of males with stroke.

click image to enlarge

Note in the case of Odds ratio we are measuring the likelihood that a stroke patient is being a male (risk factor) and not the reverse (we are not measuring the probability of getting a stroke if the patient is a male).

rasheed · Dec 12, 2009

Caution

I've seen an NBME question that requires the knowledge of this formula
A/C divided by B/D
so the mnemonic of AD/BC is not always useful.

Mondoshawan · Jan 22, 2011

rasheed said:
I've seen an NBME question that requires the knowledge of this formula
A/C divided by B/D
so the mnemonic of AD/BC is not always useful.

Isn't that the same thing in the end?
A/C divided by B/D
=
A/C times D/B
=
AD/BC

I think your mnemonic is pretty good

life9 · Apr 29, 2011

"Not in the case of Odds ratio we are measuring the likelihood that a stroke patient is being a male (risk factor) and not the reverse".

what do you mean by" not the reverse"??

rasheed · Apr 29, 2011

life9 said:
"Not in the case of Odds ratio we are measuring the likelihood that a stroke patient is being a male (risk factor) and not the reverse".

what do you mean by" not the reverse"??

Odds Ratio: measuring the odds of a risk factor when you already have the disease, i.e. you already have stroke, what's the likelihood that it was caused by male sex. It starts with the disease and ends with risk factor.

While Relative Risk and Attibutable Risk: it starts with the risk factor and ends with the disease, i.e. if you are male then what's the likelihood you'll get stroke.

Odds Ratio

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