st: No observations in stcox models

[Barth Riley <barthriley@comcast.net>]

Dear list

I am running a series of Cox regression models using stcox in Stat 11. I 
am obtaining the error message "No observations," despite the fact that 
the effective sample size (excluding missing values on all predictors 
and the failure variable) is between 150 and 550. There is also 
variability on all model variables. I should note that some of the 
predictors are categorical/ordinal and thus separate dummy variables for 
each category are being included in the model via the xi command. Could 
missing categories cause this error? Are there other factors to consider 
in determining the effective sample size for a Cox  model?

Thanks in advance

Barth


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