03-21-2018 07:25 PM
I am trying to use contrast statements in proc logistic to show estimates at different levels of X, and that the linear relationship between my dependent and independent variable isn’t constant.
I was able to find documentation here:
I just have a few questions:
Help on any of the questions is greatly appreciated!
03-21-2018 09:32 PM
1. Can you show your calculations? Control variables cancel each other out because that's not the unit you're increasing or checking for a change so when you subtract the two, they 'disappear'.
|log(Oddsx+1/Oddsx)||=||LogOddsx+1 - LogOddsx|
2. I believe it means that its the intercept*1 which is just the intercept
3. Don't know
TBH I wouldn't bother with Estimate statements.
As it states this is much easier with the ODDSRATIO statement and I'd use that instead.
Beginning in SAS/STAT 9.22 in SAS 9.2 TS2M3, you can do this more easily with the ODDSRATIO statement. Use the AT option to specify the starting value of the range over which the odds ratio should be computed. Include the UNITS statement to specify the amount of change over which the odds ratio should be computed. Without the UNITS statement, the odds ratio estimates the change in odds for a 1 unit increase in the variable. The following statements estimate the change in odds for a change in X from X=3 to X=4. The UNITS statement could be omitted in this case since a 1 unit change is requested.
I'll move this to the Stats forum so someone with better answers can help
03-23-2018 05:23 PM - edited 03-23-2018 05:40 PM
I figured out what was wrong with my calculations...I was dividing the log odds and then exponentiating, rather than exponentiating the log odds to get the odds, and then dividing by the odds to get the odds ratios.
Yea, I think your right...the odds ratio statements are easier. I'm not really sure the utility or advantage of using the estimate statements.
Thanks for your help!
03-23-2018 05:42 PM
Estimate existed before the ODDSRATIO statement, I think they leave it in for backwards compatibility and it can do some complex estimates that you can't do in others.
I've moved this post to the Stats forum so hopefully that helps. It's under Analytics, SAS Statistical Procedures.