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P-value less than 0.05 but confident limits cover 1?

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P-value less than 0.05 but confident limits cover 1?

Hi there

I'm doing a conditional logistic regression on a categorical variable with 3 levels (0, 1 and 2). The highest level vs the reference level gave me a p-value of 0.0285 which is significant but the Odds ratio estimates is (0.295, 1.064) that covers 1.


Any idea why this is the case?


p.s. this is a case/control study with 195 matched pair.


Thanks a lot!


Super User
Posts: 19,832

Re: P-value less than 0.05 but confident limits cover 1?

Post your code for the regression.

Super User
Posts: 10,041

Re: P-value less than 0.05 but confident limits cover 1?

If I were you , I would only trust confidence limitation .i.e. you can't make a deal that odds> 1 .

Xia Keshan

Frequent Contributor
Posts: 136

Re: P-value less than 0.05 but confident limits cover 1?

IMO the way the confidence interval is estimated depends on the procedure and options invoked, but in some cases the size of the confidence interval may depend somewhat on how many other exclusively different levels there are in that categorical effect, whereas the significance of a particular level does not (so much). If my understanding is correct, then the significant p-value evidence is the stronger of the two.

E.g. the CI around a trinomial proportion estimate is about 1.33 times that of an otherwise equivalent binomial estimate. That scale factor increases to about 1.66 for 4 outcomes or higher. 

Or...maybe you inadvertently performed a one-sided test for the level p-vaalue? Is that possible?

Hope that helps.

Cheers.

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