Final Assignment due: December 16, 1998

Fall, 1998

DUE: December 16, 1998

Variable #	Variable Name	Code	Coding
1	Treatment	treat	standard=1, test=2
2	Large Cell	cell1	large=1, other=0
3	Adeno Cell	cell2	adeno=1, other=0
4	Small Cell	cell3	small=1, other=0
5	Squamous Cell	cell4	squamous=1, other=0
6	Survival Time	survtime	(days) integers
7	Performance Status	perform	0=worst, …, 100=best
8	Disease Duration	sicktime	(months) integers
9	Age	age	(years) integers
10	Prior Therapy	priotx	none=0, some=10
11	Status	cstat	0=censored, 1=died

1. 
   Run all univariate analyses for assessing the influence of each covariate on survival (survtime). You would use several invocations of proc phreg for this purpose.
   

2. 
   Summarize your results in the form of a table provided below.
   

Table 1: Single covariate regression models
COVARIATE	-2log L	CHI-SQUARE (p-value)	Hazard ratio	95% CI
none	1011.768
treat
cell1
cell2
cell3
cell4
perform
sicktime
age
priortx

3. 
   Follow the model building strategy that we discussed in class. Table 1 was your first step (STEP 1) towards building a multivariable model. Notice that the cell type has four indicator variables. Use the cell1 (large cell) as your reference category in the multivariate model.
   

4. 
   Attach the (one page) printout of the multivariable model that you considered following STEP 1. Call this model-1.
   

5. 
   Now go to STEP 3, removing all variables that are not significant in the multivariable model. Use the chunk test to check your hypothesis. Provide the one page printout of this model. Call this model-2.
   

6. 
   Your final step, is to consider adding (one at a time) to model-2 each covariate not considered in STEP 1. This would involve a series of tests, which you should summarize into the following table.
   

Table 2: Mulitvariable models with variables added to model-2
Added Variable	-2log L	Chi-square (p-value)
Base model-2
+ + + + +

Does this change your model-2?

7. 
   What is the hazard ratio that compares persons with adeno cell type with persons with large cell type? Explain your answer using the general hazard ratio formula for the Cox PH model.
   

8. 
   What is the hazard ratio that compares persons with adeno cell type with persons with squamous cell type? Explain your answer using the general hazard ratio formula for the Cox PH model.
   

9. 
   Is there an effect of treatment on survival time? Explain briefly.