[R] Interval censored Data in survreg() with zero values!

Terry Therneau therneau at mayo.edu
Mon Dec 29 15:17:44 CET 2008

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My endogenous variable is not a time depending variable but percentages
which naturally are censored in the interval [0,100]. Unfortunately many
data points are 0 or 100 exactly. The rest of the data is asymmetrically
distributed. So I would like to apply a two-limit tobit, regressing the
(endogenous variable) on several explanatory variables.  

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  Censoring is a limit in the observation process: right censored at 100 means 
that "the true y value is > 100, but we did not observe the exact value".  You 
have binomial data with 0 <= y <= 100, which is not a constraint on the 
observation process.
   You should be using glm with a binomial family.  
   	Terry T

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