Estimating By Percentages
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"Remember, it's Ready, Aim, Fire; any other sequence is
- Bryce's Law
Having been involved with the systems methodologies field for over 30 years I
have been occasionally asked what percentage of time in a project should
typically be devoted to a specific phase of work, for example a Phase 1
Feasibility Study, Phase 2 Systems Design, etc. Basically, the reason the person
wants to know this is to use it as a means for estimating the remainder of the
project. For example, if I were to say Phase 1 represents 10% of the overall
project, they would simply multiply the amount of time spent in Phase 1 by ten.
This is an unreliable approach for estimating which is why I usually balk at
giving out such figures.
Systems development projects vary in size from large to small and although
statistics should certainly be maintained, I still consider this an erroneous
approach to estimating. Instead, I recommend basing an estimate on a rough
design of the product to be built (the system), including all of its pieces and
parts, such as inputs, outputs, files, records, data elements, etc. Some of
these components may be reused from other systems, some may require
modification, and some may be entirely new. This is called estimating based on
the system's "Bill of Materials," a simple concept derived from engineering and
manufacturing. Even if a project only involves a single program (as opposed to a
major system), I would still examine the types and number of components affected
by the assignment.
Having said all of this, let me give you my spin on the proportion of work in
the typical systems development project. I have seen many companies skip through
the early phases in order to get to the programming phases which is considered
the important work. Under this scenario, programming represents 85% of the
project. Instead I advocate more time spent in the early phases for better
clarity of requirements definition and for producing better specifications for
the programmers and DBA's to follow. Under this scenario, I see as much as 60%
in the early phases involving systems analysis and design, 15% in programming,
and 25% in implementation and review. You heard right, 15% in programming. Why
the disparity? Simply because programmers have long suffered from the lack of
decent specifications and end up spinning their wheels over and over again
trying to deliver what is needed. But if you concentrate on better
specifications upfront, the guesswork is eliminated for the programmer.
Some people consider the upfront work to be somewhat frivolous, that the
"real work" is down in programming. I don't know why this is, perhaps
programming is more tangible since screens and reports can be visibly shown to
people. But I do not subscribe to this notion, and believe the vital work to be
in the early phases, but then again, I am considered a dinosaur by the "Agile"
methodology people. Regardless, if you have to build anything of substance, be
it a bridge, a skyscraper, an automobile, or a system or a single program, you
have to do your homework first, otherwise you find yourself constantly tearing
things down and rebuilding them over and over again. If we built bridges the
same way we build systems in this country, this would be a nation run by
One last word on applying percentages to project estimates, the danger here
is that you might calculate you are 90% complete; inevitably you will discover
the last 10% will take forever. So, my recommendation is to avoid the percentage
trap and consider the Bill of Materials you are going to work on instead.
If you would like to discuss this with me in more depth, please do not
hesitate to send me an e-mail.
Keep the faith.
About the Author
Tim Bryce is a writer and management consultant with
M. Bryce & Associates
of Palm Harbor, Florida and has over 30 years of experience in the field. He is
available for lecturing, training and consulting on an international basis. He
can be reached at
Comments and questions are welcome.
His writings can be found at:
"PRIDE" is the registered trademark of M. Bryce & Associates (MBA) and can be
found on the Internet at:
The "Management Visions" Internet audio broadcast is available at:
Copyright © 2008 by Tim Bryce. All rights reserved.
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Article Published/Sorted/Amended on Scopulus 2008-03-16 21:51:40 in Computer Articles