[R] survival function with a Weibull dist
Hi I am using R to fit a survival function to my data (with a weibull distribution). Data: Survival of individuals in relation to 4 treatments ('a','b','c','g') syntax: survreg(Surv(date2)~males2, dist='weibull') But I have some problems interpreting the outcome and getting the parameters for each curve. - Value Std. Error z p - (Intercept) 2.788 0.147 19.022 1.13e-80 - males2b -0.107 0.207 -0.519 6.04e-01 - males2c -0.486 0.586 -0.831 4.06e-01 - males2g 0.580 0.207 2.798 5.15e-03 - Log(scale) -1.116 0.139 -8.007 1.18e-15 - - Scale= 0.328 I know from Venables Ripley (2002) that the parameters of this function should be two: lambda = z (presumably Value in R for each treatment) alpha = k (scale in R) Survival function (S): S(t)= exp-(zt)^k I don't quite understand how to use the intercept. First I thought adding it to each other treatment value, for example: Survival Males2a (t) = exp ((intercept + 0) * t) ^ k Survival Males2b (t) = exp ((intercept + zb)* t) ^ k But the curves I get using this interpretation are not similar to my data Does anyone use this function and could help me to interpret the results? many thanks Anaid __ R-help@stat.math.ethz.ch 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.
[R] nls error in formula
Hi, I'm a new R user, with a lot of questions. At the moment I'm stoped on an error traying to fit a model: x - sandeel ## numeric data (2500-6) y - Noss ## numeric data (0-1.2) A - 0.8 B - 0.6 C - 1/4 nls( y ~ A-B*exp(-C*x)) Error in match.call(definition, call, expand.dots) : .Primitive... is not a function I'm not sure if the error is due to the formula sytax or something else. I'll appreciate any help Sylvia _ Do You Yahoo!? La mejor conexión a internet y 25MB extra a tu correo por $100 al mes. http://net.yahoo.com.mx __ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
Re: [R] nls error in formula
thank you, it worked. Sylvia --- Douglas Bates [EMAIL PROTECTED] wrote: Anaid Diaz wrote: Hi, I'm a new R user, with a lot of questions. At the moment I'm stoped on an error traying to fit a model: x - sandeel ## numeric data (2500-6) y - Noss ## numeric data (0-1.2) A - 0.8 B - 0.6 C - 1/4 nls( y ~ A-B*exp(-C*x)) Error in match.call(definition, call, expand.dots) : .Primitive... is not a function I'm not sure if the error is due to the formula sytax or something else. I'll appreciate any help Sylvia Use nls(y ~ A -B*exp(-C*x), start = c(A = 0.8, B = 0.6, C = 1/4)) instead or, preferably, nls(y ~ SSasymp(x, Asym, R0, lrc)) and read ?SSasymp for an interpretation of the estimated parameters. _ Do You Yahoo!? La mejor conexión a internet y 25MB extra a tu correo por $100 al mes. http://net.yahoo.com.mx __ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html