Subject: Re: Learning Curve; Software learning percentage.
From: "Stephen J. Turnbull" <>
Date: Tue, 04 May 2004 15:55:01 +0900

>>>>> "Taran" == Taran Rampersad <> writes:

    Taran> I'm hoping that someone can tell me what the statistical
    Taran> reference for Cost Estimation of *Software* is for
    Taran> calculation in a Learning Curve calculation.

There's the 1985 book by Gotlieb, _The Economics of Computers: Costs,
Benefits, Policies, and Strategies_.  A citation search on that might
turn up something useful.   Fred Brooks _The Mythical Man-Month_,
Yourdon's _Decline and Fall of the American Programmer_ series, and
Watts Humphrey's software engineering books contain many references to
the technical literature where various coefficients have been estimated.

The problem is that most of the relevant studies were done within
corporations on extremely proprietary data, and you probably will find
that the data could be used to calculate the coefficient you want but
it hasn't been done.

    Taran> The main problem with the Learning Curve calculation on
    Taran> software is 'Number of Units', which, with software, should
    Taran> be 1 given code reuse (Wright/Crawford). And that's the
    Taran> interesting part, given licensing. It's probably apparent
    Taran> where I'm going with this...

No, not at all.

The learning curve as defined by industrial economists is about the
decrease in cost associated with mass production.  That is, you would
expect that the cost of blank CD-Rs would fall as they are produced in
their billions, and this can be fit to production and price data (or
unit, even marginal, cost data, if you can get it) to produce an
exponent for the learning curve.  The usual generator is learning-by-
doing, of which the "muscle memory" associated with a martial art or
playing a musical instrument is the prototypical example---ie, we're
talking about _exact_ repetition.

Software engineering doesn't work that way; rather, it's all about
setting up the conditions under which something like learning-by-doing
can take effect.  But the learning curve as such has assumed that
problem away; it assumes you know _how_ to mass produce whatever it
is, and then allows you to estimate the long-term cost savings from
implementing mass production.  But we don't even know how to produce
custom software efficiently yet....  :^)

Institute of Policy and Planning Sciences
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