[R] package "sensitivity" - sobol2002 indices

[Duarte Viana]

Hello all,

In the following example, one sobol index for one parameter (the first
order index for parameter b) is larger than 1. Shouldn´t the indices
have a range of [0,1]?

# Code for a decoupled approach example:

X1<-data.frame(a=runif(100,20,30),b=runif(100,0.1,0.5))
X2<-data.frame(a=runif(100,20,30),b=runif(100,0.1,0.5))

library(sensitivity)

x<-sobol2002(model=NULL,X1,X2,nboot=100)

resp<-x$X$a*x$X$b   # Example of model output

tell(x,y=resp)

print(x)

# End

Result

Call:
sobol2002(model = NULL, X1 = X1, X2 = X2, nboot = 100)

Model runs: 400

First order indices:
    original        bias std. error  min. c.i. max. c.i.
a 0.08852067 -0.01317529  0.1227359 -0.2126156 0.3132482
b 1.24009414  0.01207408  0.4018650  0.2074935 1.8574080

Total indices:
   original         bias std. error  min. c.i. max. c.i.
a 0.1172252  0.018504397  0.1501931 -0.1456118 0.4896815
b 0.4323300 -0.004814019  0.2692777 -0.1669219 1.0103819



What am I doing wrong? Or the approach has some limitation that I
might be disregarding?
Thanks for any clarification on this.

Duarte Viana