Jump to content


Photo

stepwise text

covatiate

  • Please log in to reply
4 replies to this topic

#1 Crystal

Crystal

    Newbie

  • Members
  • Pip
  • 7 posts

Posted 05 July 2022 - 01:18 AM

Dear all,

I have a problem about the Stepwise run model. I built a POP PK model, after I finished covariates stepwise, everything seems to be good, but when I check the ResultsTextOutput—Stepwise Text, it confuses me that the criterion of stepwise forward turn from 3.841 into 5.991 from cstep010 to cstep015Add P value=0.05? Does anyone know why?

Thanks a lot.

 


Edited by Crystal, 05 July 2022 - 06:20 AM.


#2 cradhakr

cradhakr

    Advanced Member

  • Members
  • PipPipPip
  • 55 posts

Posted 05 July 2022 - 03:54 AM

Hi Crystal,

 

This is the explanation for your question

 

• The LRT compares two likelihoods • For nested models the difference of two log likelihoods is asymptotically chi-squared distributed: – For 1 parameter difference (1 degree of freedom) the critical value from the chi-squared distribution is ‘3.84’ (P=0.05) \

 

http://holford.fmhs....e-modelling.pdf

 

The attached link could be of use to you.

 

Thanks

Chandramouli (Mouli)


  • Crystal likes this

#3 Crystal

Crystal

    Newbie

  • Members
  • Pip
  • 7 posts

Posted 05 July 2022 - 06:19 AM

Hi Crystal,

 

This is the explanation for your question

 

• The LRT compares two likelihoods • For nested models the difference of two log likelihoods is asymptotically chi-squared distributed: – For 1 parameter difference (1 degree of freedom) the critical value from the chi-squared distribution is ‘3.84’ (P=0.05) \

 

http://holford.fmhs....e-modelling.pdf

 

The attached link could be of use to you.

 

Thanks

Chandramouli (Mouli)

 

Thanks, Chandramouli for your help, I really appreciate it.
 



#4 cradhakr

cradhakr

    Advanced Member

  • Members
  • PipPipPip
  • 55 posts

Posted 05 July 2022 - 08:36 AM

HI Crystal,

 

Forgot to add the explanation - With RACE you might have 2 levels and the p value is 0.05

 

with

df =2 it is - 5.991465.

df=1 it is - 3.841459

 

Thanks

Mouli


  • Crystal likes this

#5 smouksassi1

smouksassi1

    Advanced Member

  • Members
  • PipPipPip
  • 200 posts
  • LocationMontreal

Posted 05 July 2022 - 08:39 AM

you can use R to know what are the thresholds:

 

> qchisq(1-0.05,1:5)
[1]  3.841459  5.991465  7.814728  9.487729 11.070498
> qchisq(1-0.01,1:5)
[1]  6.634897  9.210340 11.344867 13.276704 15.086272
> qchisq(1-0.001,1:5)
[1] 10.82757 13.81551 16.26624 18.46683 20.51501
 
the above cover p = 0.05, 0.01 and 0.001
for 1 to 5 degrees of freedom
 
 
Samer

  • Crystal likes this




0 user(s) are reading this topic

0 members, 0 guests, 0 anonymous users