turn on suggestions

Auto-suggest helps you quickly narrow down your search results by suggesting possible matches as you type.

Showing results for

Find a Community

- Home
- /
- SAS Programming
- /
- SAS Procedures
- /
- Interpretation of coefficients in PROC LOGISTIC fo...

Topic Options

- RSS Feed
- Mark Topic as New
- Mark Topic as Read
- Float this Topic for Current User
- Bookmark
- Subscribe
- Printer Friendly Page

- Mark as New
- Bookmark
- Subscribe
- RSS Feed
- Permalink
- Email to a Friend
- Report Inappropriate Content

05-27-2018 12:08 AM - last edited on 05-29-2018 01:51 PM by Rick_SAS

Hello all,

Can some one explain the following question?

The following LOGISTIC procedure output analyzes the relationship between a binary response and an ordinal predictor variable, wrist_size Using reference cell coding, the analyst selects Large (L) as the reference level.

Analysis of Maximum likelihood estimates

Parameter DF Estimate standard error Wald Chi-sq Pr>Chisq

Intercept 1 -1.0415 0.4749 4.8101 0 .0283

wrist_size M 1 1.1234 0.4989 5.0697 0.0243

wrist_size S 1 1.6078 0.5478 8.6133 0.0033

**What is the estimated logit for a person with large wrist size?**

** **

- Mark as New
- Bookmark
- Subscribe
- RSS Feed
- Permalink
- Email to a Friend
- Report Inappropriate Content

Posted in reply to SidKh

05-27-2018 02:30 AM

Always a good idea to post your code. Gives us a lot of information and makes it easier to help you.

You can get the desired quantity by using the ESTIMATE Statement like this

`estimate 'Coef for wrist_size L' wrist_size -1 -1;`

- Mark as New
- Bookmark
- Subscribe
- RSS Feed
- Permalink
- Email to a Friend
- Report Inappropriate Content

Posted in reply to draycut

05-27-2018 04:22 AM

The answer to the question is -1.0415 , the value of intercept which is a bit confusing.

Can someone explain this?

- Mark as New
- Bookmark
- Subscribe
- RSS Feed
- Permalink
- Email to a Friend
- Report Inappropriate Content

Posted in reply to SidKh

05-27-2018 07:05 AM

According to SAS documentation about parameterization method.

There is not a column of Large (L), which means its parameter should be zero. Therefore, its logit = parameter estimator of intercept.

- Mark as New
- Bookmark
- Subscribe
- RSS Feed
- Permalink
- Email to a Friend
- Report Inappropriate Content

Posted in reply to Ksharp

05-27-2018 04:15 PM - edited 05-27-2018 04:17 PM

@Ksharp provides some important information regarding how SAS handles categorical (CLASS) variables in its modeling. One level will always have a coefficient of zero, making the true value of the coefficient for this level = zero + intercept (for a simple one-way design), while the other variables will have a coefficient = (coefficient shown) + intercept (for a simple one-way design).

A better way to estimate the effect of CLASS variables in SAS is to use the LSMEANS command, and then this problem goes away. Each level (even the one with the zero coefficient) is shown with the math above computed for you.

If I may be so bold, you have entitled two recent posts "Statistics", and "Statistics" is a very very very very broad topic, and not a good title. You would be wise to provide more meaningful (and not so broad) title such as "Coefficients in PROC LOGISTIC".

--

Paige Miller

Paige Miller