[R] Is possible, on biological grounds, suggest to fitdistr (MASS library) that the estimated parameters must be between two values?

drbn drbn at yahoo.com
Thu Oct 30 10:53:55 CET 2008

Sorry if it is a silly question, I haven't found documentation on this and I
don't know if it is possible.

library(MASS) ## for fitdistr 
library(msm) ## for dtnorm 

#prepare truncated normal distribution
dtnorm0 <- function(x, mean, sd , log = FALSE) { 
   dtnorm(x, mean, sd, 105, 135, log) 


#Generate normal distribution with the TRUE population mean (day 106 of the
year) that I don't know a priori
x <- rnorm(100, mean=106, sd=40)  

#truncated sample simulating those records that I was able to observe
x<-x[x>105 & x<=135] 

#fit truncated normal distribution to the data
fitdistr(x, dtnorm0, start = list(mean = mean(x), sd = sd(x))) 

The result of the estimated true mean=132.8, sd=25.9, far from the true

Can I, on biological grounds, suggest to fitdistr that the mean must be a
value, for example, between 90 and 110?



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