DATA Step, Macro, Functions and more

Strange observations in N-way anova

Accepted Solution Solved
Reply
Occasional Contributor
Posts: 12
Accepted Solution

Strange observations in N-way anova

Hello,

 

I have run into a strange problem. I am running N-way anova and what I have found out is if i change the order of the variables that I am using in the anova, then the P-values are changing

 

E.g. when I run the below procedure

 

ods noproctitle;
ods graphics / imagemap=on;

proc glm data=WORK.INTERNETDATA;
class Exits Continent Sourcegroup Uniquepageviews Bounces Visits;
model Timeinpage=Exits Continent Sourcegroup Uniquepageviews Bounces Visits /
ss1 ss3;
lsmeans Exits Continent Sourcegroup Uniquepageviews Bounces Visits /
adjust=tukey pdiff=all alpha=0.05 cl;
quit;

 

The value of Sourcegroup is significant i.e. 0.0037

 

Now when i change the sequence of the variable Bounces to something like this

 

ods noproctitle;
ods graphics / imagemap=on;

proc glm data=WORK.INTERNETDATA;
class Bounces Exits Continent Sourcegroup Uniquepageviews Visits;
model Timeinpage=Bounces Exits Continent Sourcegroup Uniquepageviews Visits /
ss1 ss3;
lsmeans Bounces Exits Continent Sourcegroup Uniquepageviews Visits /
adjust=tukey pdiff=all alpha=0.05 cl;
quit;

 

The value of the variable Souregroup is no longer significant i.e. 0.0752

 

Can somebody tell me why is this occuring.

 

Thanks and regards,

 

Aditya


Accepted Solutions
Solution
‎10-04-2016 05:01 AM
Super User
Posts: 10,041

Re: Strange observations in N-way anova

Posted in reply to AdityaKir
It is difference between SS3 and SS1.

If you only use SS3 , you will get the same P-value , otherwise if you use SS1 ,you will get different one.


proc glm data=sashelp.class;
class age sex;
model weight=age sex/solution ss3;
run;

proc glm data=sashelp.class;
class age sex;
model weight=sex age/solution ss3;
run;

View solution in original post


All Replies
Solution
‎10-04-2016 05:01 AM
Super User
Posts: 10,041

Re: Strange observations in N-way anova

Posted in reply to AdityaKir
It is difference between SS3 and SS1.

If you only use SS3 , you will get the same P-value , otherwise if you use SS1 ,you will get different one.


proc glm data=sashelp.class;
class age sex;
model weight=age sex/solution ss3;
run;

proc glm data=sashelp.class;
class age sex;
model weight=sex age/solution ss3;
run;

☑ This topic is solved.

Need further help from the community? Please ask a new question.

Discussion stats
  • 1 reply
  • 201 views
  • 0 likes
  • 2 in conversation