Dear All,
 
I am working on a time series of hourly river flow measurements from 2000 - 2003  and have been trying to compute the extremum index from the original series as well as a new series from  sampling with replacement . The extremum Index produced from the original data series looks  fine but sadly, a strange value of index is given from the sampling. The flow measurements are in range of 0.1 to 35m3/s and are stored in data frame with the codes and  results are as follows:
 
##########################
 
### Codes   ###
attach(data)
 
# Estimates of extremum index 
 
library(evd)
library(boot)
set.seed(101)
 
threshold <- 15

ej <- exi(data$flow, u=threshold)                                       # Extremum Index computed from the original series of river flow
ei <- exi(sample(data$flow, replace=T), u=threshold)         # Extremum Index computed from sampling of the original flow series with replacement
ei; ej
mean(ei); mean(ej)
 
#######################
 
#### Results ####
ei = 0.4
ej = 1
mean(ei) = 1.023
mean(ej) = 1.014
 
#######################
 
I would  expect that the results for both index should be slightly similar as the features of both original & sampling series are more or less the same as highlighted by their sample mean and so, could  anybody please advice me on this matter?
 
Thank you,
Fir
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