Re: standardized odds ratio interpretation

Posted by Bruce Weaver on Jun 23, 2016; 6:25pm
URL: http://spssx-discussion.165.s1.nabble.com/standardized-odds-ratio-interpretation-tp5732518p5732519.html

I assume this is a follow-up to your earlier question (http://spssx-discussion.1045642.n5.nabble.com/Standardized-odds-ratios-td5732487.html).

How exactly did you obtain the standardized results you show below?  Based on the earlier thread, I'm guessing you converted both explanatory and outcome variables to z-scores before estimating your model.  That seems to me like a nonsensical thing to do when you have categorical variables.  (I'm not even sure how you would go about doing it for the 4-level variable.)  

In the original thread, I thought you were wanting to convert continuous (explanatory) variables to z-scores so that the odds ratio for a continuous variables showed odds ratios for a 1-SD increment in that variable.  I could imagine someone wanting to do this, although my preference would be to report odds ratios for some practically important increment in X that does not change from sample to sample (as the SD does).  

HTH.

Greg wrote

I was hoping to get some clarification in terms of interpreting a set of standardized odds ratios (which SPSS calculated while running binary logistic regression). The following is a small hypothetical example of the results ( I will post the unstandardized and standardized results.)

Unstandardized results

                  beta      odds ratio
Group A:   -1.149     0.317
Group B:   -0.839     0.432
Group C:   -1.340     0.262
(group d reference group)
(dependent variable is binary: 1: happy/ 0: not happy

Standardized results

                  beta      odds ratio
Group A:   -0.433     0.648
Group B:   -0.339     0.713
Group C:   -0.119     0.888
(group d reference group)
(dependent variable is binary: 1: happy/ 0: not happy

Based on the unstandardized results, the odds of being happy for group C are 73.8% lower than those of group b (56.8%). Therefore, group b has higher odds of being happy than the odds of group c.

Based on the standardized results, the odds of being happy for group C are 11.2% lower than those of group b (28.7%). Therefore, group c has higher odds of being happy than the odds of group b. (I understand that this refers to standard deviation units.)

Is the above correct? This is the first time I'm using standardized odds ratios.

Also, the odds ratio (in terms of absolute numbers) for Group c is the lowest in the unstandardized version, but the highest in the standardized. Is this normal? (based on the hypothetical example I provided).

Thank you in advance for your help!