Re: Odds Ratio - Adjusted OR

Posted by Bruce Weaver on Dec 11, 2011; 1:13am
URL: http://spssx-discussion.165.s1.nabble.com/Odds-Ratio-Adjusted-OR-tp5065253p5065283.html

For logistic regression, it is conventional to code the dependent variable 1=Yes and 0=No.  For CROSSTABS, it usually works out better (meaning you get the odds ratio you want) to have 1=Yes and 2=No.  So it may be that you're getting loused up by that difference.  Why not use LOGISTIC REGRESSION to get both your crude and adjusted odds ratios?  To get the crude (unadjusted) OR for a variable, enter it as the only explanatory variable.  

HTH.

John wrote

Hi,

I would appreciate any help from the experienced here.

I have alcohol drinking as the dependent variable. I need OR for Age, Sex,
cigarette smoking, depression as independent variables.

All are categorical variables as they have been coded

When I used Alcohol vs each of the above variables, my OddsRatios  were
Age group 1 1.02
Age group 2 0.97
Age group 3 - reference group in this category
______________
Sex (Male/ Female): 0.85
_____________
Cigarette (Yes/No): 3.54
_____________
depression (Yes/No) 1.74

I used cross tabs, checked risk in the crosstab statistics - I got the
above odds ratios thus.

______________________________________________________
I wanted adjusted ratios for the same variable in the same order. I used

click Analyze --> click Regression -> click Binary logistic -> enter in
Dependent variable ( alcohol) -> enter in covariates  (age, sex, cigarette
smoking, depression as independent variables) -> click categorical ->
enter in categorical covariates age, sex, cigarette smoking, depression ->
last as reference category -> click continue -> In options check CI for exp
(B) 95% -> check display at each step -> In probability for stepwise entry
(0.05) , removal (0.10) (default values) -> in classification cutoff 0.5
(default value this one also) -> Maximum Iterations (20) (default value) -
> check include constant in model -> click on continue -> click on ok ->
from output, I am choosing Exp(B) as adjusted odds ratio

From the output the adjusted odds ratios were (I am giving the numbers
below Exp(B) in the output tables)
Age group1 1.12
Age group2 1.06
Sex 1.08
cigarette smoking 0.73
depression 0.71

My questions for the group:

1, Am I doing the correct procedure  in SPSS by using cross tabs (risk)
for odds ratios and logistic regression (for adjusted odds ratios)? All I
need are the odds ratios and the adjusted odds ratios.
2, Obviously the main problem is the numbers for cigarette smoking and
depression are so different for odds ratio and adjusted odds ratio. Can
the adjusted ratio be so much different than odds ratio?

I am using the same dataset. The sample size of the total data set is big
(n=5500) and the n for each of the answers of each variables are big
enough. There is no problem with the sample sizes for each variable. I am
using point and click buttons in SPSS 19 version, unfortunately I don't
know coding to use syntax for output.

I will appreciate any help. Thanks,

John

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