
50 ◾ Software Metrics
Using the same model will generally yield dierent results, if we use
dierent prediction procedures. For instance, in Example 2.13, the model
parameters supplied by a friend may be very dierent from those supplied
by the automobile association. is notion of changing results is especially
important when predicting soware reliability.
EXAMPLE 2.14
A well-known reliability model is based on an exponential distribution for
the time to the ith failure of the product. This distribution is described by the
formula
Ft e
Ni at
()
=−
−−+
1
1
Here, N represents the number of faults initially residing in the program,
while a represent ...