cox regression (where observations are not independent)

Posted by Paul Mcgeoghan on Aug 22, 2006; 10:26am
URL: http://spssx-discussion.165.s1.nabble.com/cox-regression-where-observations-are-not-independent-tp1070471.html

Hi,

I have a customer who has carried out the following experiment.
He has data as follows:

     Pt_ID Reg_Seq Regimen           Gender Risk_Factor   Ethnicity Employ
Duration Disc_Stat
         1             1                51                           1         3
      1        1          141.57               2
         2             1                51                           1         3
      1        2          211.57               2
         3             1                47                           1         3
      1        1          103.71               1
         3             2                49                           1         3
      1        1           98.57               2
         5             1               127                           1         3
      1        1           21.57               1
         5             2               129                           1         3
      1        1            4.43               1
         5             3               148                           1         3
      1        1           17.43               1

He is looking at Duration until patient gets the symptom which is Disc_Stat=1

Reg_Sequence represents the ordered number of regimen sequence.
Regimen Sequence is a combination of drugs given to the patient.
Patients in the sample could change drug regimen composition and each change
marked an
increase in the number of Reg_Sequence.

The duration will reset to zero with each change of regimen sequence.

I think there could be a problem with the design of the study (the possibility
of a carryover effect from previous Regimen sequences)

What type of analysis can be done on the above as the assumptions of Cox
Regression are violated?
Can the customer just take the last Regimen sequence and analyse that using Cox
Regression?

Paul


==================
Paul McGeoghan,
Application support specialist (Statistics and Databases),
University Infrastructure Group (UIG),
Information Services,
Cardiff University.
Tel. 02920 (875035).