Re: Inspections Was: RE: [AM] ANN: Mashing Deadly Myths

(esrponding to Scott P)

> It also isn't clear that having both pairs of eyes looking at
> the code together is more effective at defect removal than
> having one write it and the other read it after the fact.  As
> mentioned in a previous posting, the reported numbers for
> defect reductions from using pair programming are toward
> the low end of typically reported numbers for single-reader
> inspections.

That particular study reported 15% reduction in defects.
I've found figures quoted in Boehm and Turner for 4
other studies; figures quoted for defect reduction are
0%, 30%, 60% and 61%.  Clearly the circumstances of the
studies differ and a more detailed reading of the studies
may help.  For example, the "0%" defect reduction seems
to be derived from figures in different domains, where one
domain reported increased defects, one reported fewer
defects, and two domains reported no change in defects.

However, the "more defects" figure was from a single
project in the aerospace domain, while the "fewer
defects" figure was from 15 projects in the e-Business
domain.  The "no change" arises from 4 'software'
projects and 5 'telecoms' projects.  Thus the "0%"
figure is from a study where, of the projects reporting on 
defect rate, 4% showed more defects and 60% showed
fewer defects.  I would hazard a guess that the most significant
factor in this study would be the maturity of process against
which the agile process was being compared.  That
must remain a guess, because the data is not recorded 
other than by naming the 'domains'.

In short, the 15% just might be toward the low end of
the typical figures for defect reduction in agile processes.


>  This wouldn't be surprising - the single inspector has no
> other opinion to defer to, a member of a pair may not raise
> an issue because she thinks the other member knew what
> she was doing.  If you've got two people working together
> and they have different answers to a given question, there's
> a non-zero probability that the one favoring the wrong
> answer will convince the one who actually knew the right
> answer, rather than vice versa.

All these things are possible.  On your second point, the 
member of the pair *should* raise an issue if the result is
not understood, yet of course there will be times when this
doesn't happen.


Paul Oldfield

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