On Jul 17, 2009, at 12:52 AM, Sean Brummel wrote: > This conversation is digressing... Here is my question, what does > the value from the predict function mean? AS STATED IN MY CODE. Try > running the example that I gave. > > predict(model,type=c("response"))[1]=?????????
Look at the help page and work through the examples: Expected survival time, in the units being measured for time, of an individual with the same covariates as the first subject. It is not a probability. If you want a probability rather than a time, you need to use type ="quantile" and then supply an appropriate set of percentiles. > > Sean > > On Thu, Jul 16, 2009 at 8:27 PM, David Winsemius <dwinsem...@comcast.net > > wrote: > Wouldn't the "response" of a survival model be survival times? You > may want to look at survfit and survest. > > -- > DW > > > On Jul 16, 2009, at 9:19 PM, Sean Brummel wrote: > >> With type="response" in the predict funtion, I was expecting an >> expected survival time given covariates( in my dataset I have a few >> covariates but not in the example)... a natural predictor. The >> prediction function is clearly not returning a probability of >> survival at a given time since my example it is greater than one. >> >> >> Sean >> >> >> On 7/16/09, David Winsemius <dwinsem...@comcast.net> wrote: >> >> On Jul 16, 2009, at 8:19 PM, Sean Brummel wrote: >> >>> Thanks for the help but... >>> >>> I did the required transformations at the end of the code. The >>> thing that I dont understand is: Why is the predicted value (from >>> the predict function) not either the mean or median. Sorry I was >>> not clear in my explanation. >> >> >> >> ?predict.survreg >> >> >> You might get better answers if you specified even more concretely >> what you expected and more expansively why you think so. It sounds >> as though you expect predict to give you a median or mean, but this >> is not what R predict functions generally return. The predict >> function returns the estimated survival at the requested times If >> the newdata parameter is not supplied, then those times are taken >> to be those in the original dataset. >> >> >> >>> >>> Thanks, >>> >>> Sean >>> >>> >>> On 7/16/09, David Winsemius <dwinsem...@comcast.net> wrote: >>> >>> On Jul 16, 2009, at 7:41 PM, Sean Brummel wrote: >>> >>> I am trying to generate predictions from a weibull survival curve >>> but it >>> seems that the predictions assume that the shape(scale for >>> survfit) parameter is one(Exponential but with a strange rate >>> estimate?). >>> Here is an examle of the problem, the smaller the shape is the >>> worse the >>> discrepancy. >>> >>> ### Set Parameters >>> scale<-10 >>> shape<-.85 >>> ### Find Mean >>> scale*gamma(1 + 1/shape) >>> >>> ### Simulate Data and Fit Model >>> y<-rweibull(10000,scale=scale,shape=shape) >>> model<-survreg(Surv(y)~1,dist="weibull") >>> >>> ### Exp of coef and predict are the same >>> exp(model$coef) >>> predict(model,type=c("response"))[1] >>> >>> ### Here is the mean and median of the data >>> mean(y) >>> median(y) >>> >>> ### Fitted Mean and Median from survreg >>> fitScale<-exp(model$coef) >>> fitShape<-1/model$scale >>> fitScale*gamma(1 + 1/fitShape) >>> fitScale*(log(2))^(1/fitShape) >>> >>> Is this done on purpose? If so does anyone know why? >>> >>> http://finzi.psych.upenn.edu/Rhelp08/2008-October/178487.html >>> >>> -- >> >> > > David Winsemius, MD > Heritage Laboratories > West Hartford, CT > > David Winsemius, MD Heritage Laboratories West Hartford, CT [[alternative HTML version deleted]] ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.