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## #1 2013-12-09 04:31:33

extjsjquery
Member
Registered: 2013-12-09
Posts: 4

### odds ratio problem

I input a,b,c,d  use odds ratio calculator

Cases with positive outcome
Number in 1st group:    a=25
Number in 2nd group:    b=15
Cases with negative outcome
Number in 1st group:    c=18
Number in 2nd outcome:    d=30

and calculate

Results
Odds ratio    2.8889
95 % CI    1.2184 to 6.8497
z statistic    2.408
P = 0.0160

I know odds ratio is Odds ratio = (a/c) / (b/d)
my question is
what z statistic    and p mean ?

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## #2 2013-12-09 04:42:17

bobbym
bumpkin
From: Bumpkinland
Registered: 2009-04-12
Posts: 109,606

### Re: odds ratio problem

Hi;

Are you doing something like this?

I am getting an OR = 2.7777777777

Also I think you mean P rather than p.

Z scores are measures of standard deviation. P is a probability.

In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

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## #3 2013-12-09 15:39:08

extjsjquery
Member
Registered: 2013-12-09
Posts: 4

### Re: odds ratio problem

Tks for your reply.  I input a wrong number that Number in 1st group:    a=26
not 25    if 25  ,2 .777  is  right.
like formula Odds ratio = (a/c) / (b/d) ,what is the formula for probability？

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## #4 2013-12-09 21:49:58

bobbym
bumpkin
From: Bumpkinland
Registered: 2009-04-12
Posts: 109,606

### Re: odds ratio problem

Hi;

You can get a probability from the odds.

In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

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