Path: utzoo!attcan!uunet!snorkelwacker!usc!zaphod.mps.ohio-state.edu!sol.ctr.columbia.edu!cica!iuvax!smith
From: smith@iuvax.cs.indiana.edu (John W. Smith)
Newsgroups: comp.software-eng
Subject: Re: Retrospective Forecasting
Message-ID: <37392@iuvax.cs.indiana.edu>
Date: 28 Feb 90 15:19:21 GMT
References: <20406@bellcore.bellcore.com>
Organization: Indiana University, Bloomington
Lines: 30


	I think there is tremendous value in learning from the past.
I have for many years trying to understand why we in this business
consistently underestimate project times by hundreds of percent.  The
conclusion I come to is that we are for the most part completely blind
to the past.  There are two specific mistakes that I've seen
repeatedly.  
	We assume that THIS project will work as it is supposed to.  
There are a few projects where this actually happens, just enough to
sustain the belief in the possibility.  But 19 out of 20 get screwed
up in some way or another.  We may recognized that the last project
was delayed because the vendor didn't deliver the connectors on time.
So for the current project we order well in advance.  But then the
connectors get lost in the mail, and nobody followed up, so THIS
project is delayed.  If you consciously and deliberately review your
projects over a number of years, it is very obvious that the normal
mode is for things NOT to work as intended.
	The second mistake we make is to remember the time it took to
FIX the problem, but not the time it took to FIND it.  It takes half
an hour to change the number and recompile the program.  That's what
your staff will remember.  They DON'T remember the two weeks it took
to figure out that it was that particular number which was causing the
problem.
	It could be that the kind of people who are attracted to a
fast-moving and ever-changing environment such as ours are evolutionarily 
selected to NOT have a historical perspective.  But if we're trying to
manage, hence control, our environment, it is a very valuable tool
that we could make much better use of.  Although the examples I've
given pertain specifically to management rather than forecasting, the
basic ideas are no less true.