Software Estimation - part 1 of 2

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Information about Software Estimation - part 1 of 2

Published on January 29, 2014

Author: adi.dancu



A summary, some tips & tricks, after reading a book called "Software Estimation - Demystifying the “Black Art".
Should be useful for anyone who has to perform any kind of estimates, but especially useful for software developers & managers.

… a summary, some tips & tricks to remember, after reading a book called… PART 1 of 2

PART 1 of 2    What is an Estimate? What is a Good Estimate? Estimation Accuracy PART 2 of 2    Estimation Techniques How to Present Estimates How to Debate & Negotiate based on Estimates

“The process is called estimation, not exactimation.” (Phillip Armour)

Dictionary definition? 1. Tentative evaluation or rough calculation 2. Preliminary calculation of the cost of a project Source: American Heritage Dictionary, 1985 …TENTATIVE …PRELIMINARY

 Estimate – a prediction – how long a project will take / cost  Target – a statement – desirable business objective  Commitment – a promise – deliver a feature by a certain date

 Estimates are not Targets  Estimates are not Commitments

 Estimation – an unbiased, analytical process – goal is accuracy (not seeking a particular result)  Planning – a biased, goal-seeking process – goal is a particular result (specific means to a specific end)

Planning is not Estimation  Estimation is not Planning  Plans rely on estimates. Estimates higher than targets – plan has higher risk level.

When asked for an estimate, determine if you’re actually supposed to: - estimate - make a commitment - figure out a plan on how to hit a target

“There’s no point in being exact about something if you don’t even know what you’re talking about.” (John von Neumann)

Single-Point Estimates (e.g. 18 weeks)  useless – no probability degree  more likely a target masquerading as an estimate (or an estimate stripped of probability info) Accurate Estimate  probability factor attached  18 weeks with 10% chances of success  18 to 24 weeks For single-point estimates, probability is not 100%. Always ask what the probability is.

 Project success – good project control  Criteria for a good estimate – ability to support project success, through project control  Working definition of a good estimate:  A good estimate is an estimate that provides a clear enough view of the project reality to allow the project leadership to make good decisions about how to control the project to hit its targets

   18 weeks 18 to 19 weeks 18 to 24 weeks  Avoid using artificially narrow ranges  The ranges in your estimates must represent your confidence in your estimates  Pressure to make ranges narrower?  Verify that the pressure is actually coming from an external source – not from yourself

Arguments against over-estimation    Parkinson’s Law Student Syndrome Positive stress Arguments against under-estimation     Reduced effectiveness of project plans Statistically reduced chance of on-time completion Poor technical foundation Destructive late-project dynamics DON’T INTENTIONALLY UNDERESTIMATE! The penalty for underestimation is almost always more severe than the penalty for overestimation.

     Improved project status visibility Higher quality Better coordination with nonsoftware functions Increased credibility for the dev team Early risk information A mismatch between business targets and estimates: early and valuable risk information that the project might not be successful. Take corrective action early, when it can do some good.

Inaccurate information about the project / team  Trying to estimate a moving target  Estimates – more accurate as project progresses. More refined software definition = more accurate estimate  Early in the project, estimates can be off to up to 4x   In the first 30% of the project estimation accuracy improves rapidly – from ±4x to ±1.25x 

Consider the effect of the „Cone of Uncertainty” on the accuracy of your estimate –YOU CANNOT HAVE MORE ACCURACY THAN IS POSSIBLE at current position.  Use predefined uncertainty ranges in your estimates.  Do not assume the cone will narrow itself. Force the cone to narrow by removing sources of variability.


 Unfounded Optimism  Developer estimates – statistically 20-30% off DON'T REDUCE DEVELOPER ESTIMATES – THEY'RE PROBABLY TOO OPTIMISTIC ALREADY  Subjectivity and Bias  „Intuition” and „quessing”, off-the-cuff estimates DON’T GIVE OFF-THE-CUFF (IMPROMPTU) ESTIMATES. EVEN A 15 MINUTE ESTIMATE IS MORE ACCURATE  Accuracy versus Precision  354.5 days versus 1 year MATCH THE NUMBER OF SIGNIFICANT DIGITS IN YOUR ESTIMATE (ITS PRECISION) TO YOUR ESTIMATE’S ACCURACY

End of PART 1 of 2 … coming soon… PART 2 of 2  Estimation Techniques  How to Present Estimates  How to Debate & Negotiate based on Estimates Bio: Software Estimation: Demystifying the Black Art by Steve McConnell Microsoft Press, 2006

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