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Phreg multivariable model - hazard ratio is 1 and significant

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Contributor
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Phreg multivariable model - hazard ratio is 1 and significant

I ran a Proc phreg with 2 continuous variables and 3 binary variables. One of the continuous variables (ranges between 10 and 250) is highly significant but the HR is only 1.013. This is from the "Analysis of Maximum Likelihood Estimates" table.

Any thoughts on what might cause such results? I have a reasonable sample size of 150 observations. The binary variables have a distribution of <10 yeses and 140 "no"s

 

Super User
Posts: 768

Re: Phreg multivariable model - hazard ratio is 1 and significant

Why is a hazard ratio of 1.013 particularly small for a continuous variable thet ranges from 10 to 250? The HR is presumably for a 1 unit change in the variable (e.g. from 10 to 11). So a 10-unit change has an HR of 1.1378, and the full range of 240 units has an HR of 22.195.  Is that disappointingly low?

Contributor
Posts: 40

Re: Phreg multivariable model - hazard ratio is 1 and significant

Thank you very much for your explanation. My HR is actually exactly 1 for a variable that ranges from .1 to 1600. Would that be just displayed that way due to rounding? How can I explain that? Thanks

Contributor
Posts: 40

Re: Phreg multivariable model - hazard ratio is 1 and significant

It's 1.000 to be exact

Super Contributor
Posts: 271

Re: Phreg multivariable model - hazard ratio is 1 and significant

I think you should scale your contionous variable such that the variable you put into PHREG goes in from 0 to 10 (or of that order of magnitude).Otherwise rounding errors and errors due to numerical precision otherwise can easily get a too big impact on the interpretation of the estimates.

Contributor
Posts: 40

Re: Phreg multivariable model - hazard ratio is 1 and significant

Thank you for the suggestion. That was very helpful

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