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Software Estimation with Three point estimates September 13, 2005

Posted by Coolguy in Software Development.
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We all know theoretically,although we sometimes fail to acknowledge in practice, that project time and cost plan are guesses based on our best estimates.In some environments there there is a lot of historical data and expert knowledge around, that could be used to make that guesses as ‘educated’ as possible.Unfortunately when a type of project is being done for the first time in an organisation the chances of any guesses being correct is remote.
When someone is asked to provide a single point estimate for a parameter, there is a little chance that it will be correct.
An accurate estimate is a range of values that contains the correct value.Range is:

  • Minimum Value
  • Most likely Value
  • Maximum Value

PERT formula can be used to get to a single point estimate from these range of values:

Minimun +(4*Most likely) + Maximum

—————————————-

6

Remember precision ‘sets us up’ for later perception of failure.

If a project’s business case can stand up at the extremes of the ranges, there should not be any worry.

If the business case stands up at the optimistic end of the range, the we have a problem.

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