11-27-2012 03:19 PM
There are a number of survivor functions available, and the calculations are available for each type in the documentation under Details: PHREG Procedure>Survivor Function Estimators. There is a Breslow estimator, Flemin-Harrington estimator, and the product-limit estimator.
You should be able to check the calculation based on the formulas provided.
11-27-2012 03:31 PM
I'm trying to use the betas from the model, plug in the individual patient data into a formula with the betas and try to recreate the exact values that I get in the survival=
I think i would use this, but what do I plug in for alpha?
hi(t) = exp(α + β1xi1 + β2xik + ・ ・ ・+ βkxik)
11-27-2012 05:44 PM
I'm not sure, but here's what I'd try
The formula you have is the hazard function formula, h(t), not the survivor function.
The survivor is S(t)=S(baseline)(t)^exp(B1x.....)
from SAS docs.
You have your beta's from the output and you can get the baseline syntax in proc phreg
I don't know if you'd need to set values for the covariates or not, but that's where I'd start.
11-28-2012 05:37 AM
Expanding on Reeza's comment.
Some math thoughts: In exp(α + β1xi1 + β2xik + ・ ・ ・+ βkxik), the first term exp(α) is a constant that ends up as a multiplier of exp( β1xi1 + β2xik + ・ ・ ・+ βkxik), and is thus just part of S(baseline). You do not need alpha to calculate survivor functions.