SAS Programming

DATA Step, Macro, Functions and more
BookmarkSubscribeRSS Feed
stellapersis7
Obsidian | Level 7

Hi all,

I am student and doing a project, so I am confused about a linearity assumption of a continuous independent variable which is included in the model.

My aim is to check the graphs between gestage and estimated probability for genders male and female.

I need to check when the variable is included as 1) categorical and 2) continuous, if the linearity assumption is met.

My code is 

proc genmod data = SAS.z_final descending;

class gender  under_weight  QNO;

model under_weight = gender gestage /dist=b link=logit type1 type3;

repeated subject = QNO/ corr=cs corrw;

output out = pain pred=p resraw=r;

run;

My question is how to get the linearity assumptions for the independent variable gestage as continuous and categorical variables for gender(independent categorical variable) male and female?

3 REPLIES 3
PaigeMiller
Diamond | Level 26

For continuous X in a logistic regression, this is suggested in the SAS FASTats:

 

Linearity in the logit (or link), testingTo test for nonlinearity in the logit (for logistic models) and more generally for finding a suitable functional form for an independent variable in a generalized linear model (GLM), use the spline smoother on the variable in SAS/STAT PROC GAMPL or SAS Viya PROC GAMMOD. See the example titled "Nonparametric Logistic Regression" in the GAMPL documentation. Also see the ASSESS statement in SAS/STAT PROC GENMOD for assessing the covariate or link function in a GLM or Generalized Estimating Equations (GEE) model.

Also https://www.lexjansen.com/sesug/2019/SESUG2019_Paper-233_Final_PDF.pdf

 

https://stats.stackexchange.com/questions/169348/how-should-i-check-the-assumption-of-linearity-to-t... points to using the Box-Tidwell test.

 

Checking linearity for categorical predictor makes no sense.

--
Paige Miller
Ksharp
Super User
Paige,
Sure. I forgot the "ASSESS statement in PROC GENMOD " .

sas-innovate-white.png

Our biggest data and AI event of the year.

Don’t miss the livestream kicking off May 7. It’s free. It’s easy. And it’s the best seat in the house.

Join us virtually with our complimentary SAS Innovate Digital Pass. Watch live or on-demand in multiple languages, with translations available to help you get the most out of every session.

 

Register now!

How to Concatenate Values

Learn how use the CAT functions in SAS to join values from multiple variables into a single value.

Find more tutorials on the SAS Users YouTube channel.

SAS Training: Just a Click Away

 Ready to level-up your skills? Choose your own adventure.

Browse our catalog!

Discussion stats
  • 3 replies
  • 2185 views
  • 0 likes
  • 3 in conversation