is equal to 1. Substituting 
in the probability density function
of Eqn. (21) gives:
(24)where 
of Eqn. (21)
has been replaced by 
. Parameter 
is called the failure rate [19].
Hence, R-DOE analysis for exponentially distributed data can be carried
out by substituting 
and replacing 
by 
in the Weibull distribution.