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

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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**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 91,664

Hi;

Are you doing something like this?

http://www.youtube.com/watch?v=ITi0SxmQTO8

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.**

**I agree with you regarding the satisfaction and importance of actually computing some numbers. I can't tell you how often I see time and money wasted because someone didn't bother to run the numbers.**

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

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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**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 91,664

Hi;

You can get a probability from the odds.

**In mathematics, you don't understand things. You just get used to them.**

**I agree with you regarding the satisfaction and importance of actually computing some numbers. I can't tell you how often I see time and money wasted because someone didn't bother to run the numbers.**

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