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...u can see, the values obtained from using both functions are very similar. But, what puzzled is the warning message that i got from using nlm. Could anyone please shed some light on how this warning message come about and whether it is a cause for concern? Many thanks in advance for any advice! singyee [[alternative HTML version deleted]]

...,df.b1,df.b2) return(value) } theta.start<-c(0.01 ,-1.20, -0.0005) outcs39<-nlm(loglikcs39,theta.start,len=50) Error in nlm(loglikcs39, theta.start, len = 50) : probable coding error in analytic gradient Any light that can be shed on this would be highly appreciated. Many thanks Singyee Ling [[alternative HTML version deleted]]

...hical checks for proportional hazards assumption is often preferred to formal test as formal test based on a large enough sample (in my case is 4000 data entries), will often reject the null hypothesis of proportionality. Is that what is happening in my case? any suggestion? Thanks! kind regards, singyee ling [[alternative HTML version deleted]]

Dear R-users, I use the survsplit function in the survival package to change my data into counting-process format and the transformed format is as follow: (a) start stop event DP age .... 0 5 0 1 20 5 10 0 1 20 10 25 1 1 20 looking at the above three entries that belong to the same person, if an event happen at

Dear R-users, I am sorry if this is obvious. I am testing the proportional hazard assumptions using cox.zph. If i am not wrong, a g(t) function must be assumed. Four possibilities available in R are "km","identity" and "rank". may i know what functions of time are these transformation assuming? Thanks a lot in advance for your wisdom. kind regards, sing yee ling

Dear R-users, I am checking the proportional hazard assumption of a cox model for a given covariate, let say Z1, after adjusting for other relavent covariates in the model. To this end, I fitted cox model stratified on the discrete values of Z1 and try to get beslow estimator for the baseline cumulative hazard function (H(t)) in each stratum. As far as i know, if the proportionality assumption

...Assam) 12. Re: Building tkentry dynamicly (Sean Davis) 13. Re: returning the largest element in an array/matrix? (Henrik Bengtsson) 14. Re: POSIX time zone codes (Gabor Grothendieck) 15. Re: Building tkentry dynamicly (John Fox) 16. breslow estimator for cumulative hazard function (singyee ling) 17. Re: POSIX time zone codes (Jason Horn) 18. Re: breslow estimator for cumulative hazard function (Christos Hatzis) 19. Re: POSIX time zone codes (Gabor Grothendieck) 20. Re: (newbie) Accessing the pieces of a 'by' object (Vivek Satsangi) 21. Re: (newbie) Acces...

dear all, I would like to know whether survdiff and survReg function in the survival package work for left-truncated and right-censored data. If not, what other functions can i use to make comparison between two survival curves with LTRC data. thanks for any help given sing yee

Dear R-users, I know that a few people have asked whether survreg handles left-truncation data and the reply that i have seen so far is that it does. However, when I try to use survreg on left-truncated data, I got the following error message. > survcs3<-survreg(Surv(start,end,status)~AG, data=DPONEcs3, dist="exponential") Error in survreg(Surv(start, end, status) ~ AG, data =