
490 ◾ Software Metrics
For predicting the median time to the next failure, our procedures are
similar. For this distribution, the median is 1/λ
i
log 2 and the mean is 1/λ
i
; so,
the procedure is the same, except that all the results above are multiplied by
log 2 (i.e., by a factor of about 0.7).
Many prediction systems have been proposed, some of which use mod-
els and procedures far more sophisticated than Example 11.9. We as users
must decide which ones are best for our needs. In the next section, we
review several of the most popular models, each of which is parametric
(in the sense that it is a function of a set of input parameters). en, ...