search for: jferrer

Hello, I've had no luck finding an R package that has the ability to estimate a Tobit model allowing for heteroskedasticity (multiplicative, for example). Am I missing something in survReg? Is there another package that I'm unaware of? Is there an add-on package that will test for heteroskedasticity? Thanks for your help. Cheers, Alan Spearot -- Alan Spearot Department of Economics

...ratorio de Biolog??a de Organismos - Centro de Ecolog??a Instituto Venezolano de Investigaciones Cient??ficas Apartado 21827 - Caracas 1020A REPUBLICA BOLIVARIANA DE VENEZUELA Tel:00-58-212-5041452 --- Fax: 00-58-212-5041088 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ jferrer at ivic.ve

Hello, I would like to inlude the Q-Q plot by "qqmath" into a panel with other plots, say, using par(mfrow=c(1,2)). How can this be done given that "qqmath" refreshes the plotting window and there seems to be no series coming out of it? Thanks Serguei [[alternative HTML version deleted]]

Hi, I'm trying to aggregate date values using the aggregate function. For example: aggregate(data,by=list(weekdays(LM),months(LM)),FUN=length) I would also like to aggregate by year but there seems to be no years() function. Should there be one? Is there any alternative choice? Also, a hours() function would be great. Any tip on this? Thanks in advance! S?rgio Nunes

Hello, I have a small statistics question, and as I'm quite new to statistics and R, I'm not sure if I'm doing things correctly. I am looking at two quantitative variables (x,y) that are correlated. When I divide the data set according to a categorical variable z, then x and y are more poorly correlated when z = A than when z = B (see attached figure). In fact x and y are two

...Dipl.-Biol. JR Ferrer Paris ~~~~~~~~~~~~~~~~~~~~~~~~~~~ Laboratorio de Biolog?a de Organismos --- Centro de Ecolog?a Instituto Venezolano de Investigaciones Cient?ficas (IVIC) Apdo. 21827, Caracas 1020-A Rep?blica Bolivariana de Venezuela Tel: (+58-212) 504-1452 Fax: (+58-212) 504-1088 email: jferrer at ivic.ve clave-gpg: 2C260A95

...Dipl.-Biol. JR Ferrer Paris ~~~~~~~~~~~~~~~~~~~~~~~~~~~ Laboratorio de Biolog?a de Organismos --- Centro de Ecolog?a Instituto Venezolano de Investigaciones Cient?ficas (IVIC) Apdo. 21827, Caracas 1020-A Rep?blica Bolivariana de Venezuela Tel: (+58-212) 504-1452 Fax: (+58-212) 504-1088 email: jferrer at ivic.ve clave-gpg: 2C260A95

Hello, I am trying to get the P values from the output of a summary for lm. lm <- lm(y ~ age + sex) s <- summary(lm) I thought that I might be able to get them using a combination of scan, grep and sub. But I got stuck on the first step - being able to process "s" as a text string. I could perhaps write it to file than scan it back but there is probably an easier way to do

Hi there, I'm writing a function that calculates the probability of different outcomes of dice rolls (e.g., the sum of the highest three rolls of five six-sided dice). I'm using the "combinations" function from the "gtools" package, which is great: it gives me a matrix with all of the possible combinations (with repetitions allowed). Now I want to count the number