Prediction Based on Actual When Available
or Best Estimate (Line 20)
This is the real purpose of this model. The values on this line are selected from
Actuals by Phase (line 18) if available. These are actuals for this project. If Actuals
by Phase is not available, then the value from Estimate Based on PPB Element (line
15) is used, if available. Use the Estimate Based on Historical Effort Distribution
(line 16) if no other values are available. The prediction is then 32,430, which is the
sum of all phases. (Not to be confused with the Sum of All Fears, which is a book
by Tom Clancy.)
So how do you use a PPM with your projects?
You use PPMs to estimate or predict a critical value that cannot be measured
until later in the project??™s life. Our example showed a model to predict total effort
throughout the project life cycle. No one really knows what the total effort will be
until the project is over.
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264 n Interpreting the CMMI
We have seen a model similar to our example used to accurately predict total
effort.
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