sciplot question
On May 24, 2009, at 4:42 , Frank E Harrell Jr wrote:
Jarle Bj?rgeengen wrote:
On May 24, 2009, at 3:34 , Frank E Harrell Jr wrote:
Jarle Bj?rgeengen wrote:
Great, thanks Manuel. Just for curiosity, any particular reason you chose standard error , and not confidence interval as the default (the naming of the plotting functions associates closer to the confidence interval .... ) error indication . - Jarle Bj?rgeengen On May 24, 2009, at 3:02 , Manuel Morales wrote:
You define your own function for the confidence intervals. The function needs to return the two values representing the upper and lower CI values. So: qt.fun <- function(x) qt(p=.975,df=length(x)-1)*sd(x)/ sqrt(length(x)) my.ci <- function(x) c(mean(x)-qt.fun(x), mean(x)+qt.fun(x))
Minor improvement: mean(x) + qt.fun(x)*c(-1,1) but in general confidence limits should be asymmetric (a la bootstrap).
Thanks, if the date is normally distributed , symmetric confidence interval should be ok , right ?
Yes; I do see a normal distribution about once every 10 years.
Is it not true that the students-T (qt(... and so on) confidence intervals is quite robust against non-normality too ? A teacher told me that, the students-T symmetric confidence intervals will give a adequate picture of the variability of the data in this particular case. Best rgds Jarle Bj?rgeengen