I have a question regarding the way Gretl computes quantiles. There is probably a small
typo in the reference guide. It says that the p-th quantile q of series y with n
observations is computed as
q=y[k] +(n·p-k)(y[k+1] -y[k])
where k is the integer part of n·p. Probably this should read "where k is the integer
part of (n+1)·p".
Running the following script
clear
matrix x=seq(1,4)'
matrix p={0.25, 0.5, 0.75}
q=quantile(x,p)
print q
Returns
q (3 x 1)
1.25
2.5
3.75
Jan Annaert