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Software Estimation


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What's the difference between an estimate, a commitment, and a target
estimate=how long it will take. commitment = when you agree to finish it. target=when they want it done
What are the five steps that must be completed before you make a commitment?
Initial Concept, Product Definition, Requirements Analysis, Detailed Design, UI Design
What are the pitfalls of underestimating
-Poor team coordination
-more wasteful "off track" meetings
-frequent reestimation
-poor customer relations
-preparing a demo because real software is not done
-fixing issues with quick and dirty workaraounds to meet schedule pressure
What are the pitfalls of overestimating
Student Syndrome - developers will procrastinate and then rush and probably won't finish on time
Cardinal Rule 1 of Estimating
Do NOT make off the cuff estimates. Even a 15-minute estimate is better
Trick of estimating
Give estimates in a wide range and commit to expected. Give periodic updates on where you are in the range
Cardinal Rule 2 of Estimating
Do NOT make a commitment until detailed design is done
What are the 3 major factors in an estimate?
Project Size, Complexity, Personnel
What are the estimate multipliers in the Cone of Uncertainty?
Initial Concept - 16x
Approved Product Definition - 4x
Requirements Complete - 2.25x
UI Design Complete - 1.6x
Detailed Design Complete - 1.2x
What are the steps in the Count, Compute, Judge method?
-Count something, i.e. lines of code, tables, etc
-compute how long it will take to complete each
-use judgement as your last resort
What are the steps in structured expert judgement?
-have the ppl doing work estimate
-break project up into features
-estimate Best Case (BC), Most Like Case (MLC), and Worst Case (WC) for each feature
-keep track of actual
What are the steps of decompose and recompose
-break up into 5 - 10 pieces
-estimate BC and WC for each
-calc standard deviation (Sum(WC)-Sum(BC))/6
-calculate intervals
25% = EC -(.67xSD)
50% = EC
75% = EC + (.67xSD)
98% = EC + (2xSD)
How to tell if estimate is good
1. Product clearly defined?
2. Does it include everything?
3. Is it detailed enough to expose hidden work?
4. Was it composed using historical data?
5. Was it done by the person who will do the work?
6. Is the productivity assumption realistic?
7. Does it include BC, EC, WC?
8. Is WC really the WC?
9. Have the assumption been documented?
10. Has any thing changed since the estimate was done?

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