Practical Software Estimation Measurement

Ask Carol: How Many Projects Create a "History?"

Dear Carol:

As a project manager who is new to formal project estimating, I’ve been hearing about the importance of having project histories available for accurate estimating.  We just purchased SLIM-Estimate but we don’t have any project history.  Can we still use SLIM, and how many projects do we need before we can get accurate estimates?

– PM in Atlanta

Dear PM:

You may have heard that “history repeats itself” and the adage is true in software development.  Completed projects where the actual software size, effort hours, duration and cost are often the best predictors of future performance on projects – and your own project history gives accurate indicators of how your corporation performs.  However, the majority of QSM clients who purchase SLIM-Estimate start out with little or none of their own project history.  The good news is that the SLIM tool comes preloaded with productivity, duration, staffing, and effort hours trend lines based on thousands of completed real life projects, and delineated by industry and type of project.  When you do an estimate using SLIM, the Monte Carlo simulation models are run, and the results are compared against trend line graphs so that you can see how your estimate of effort, duration, staffing and cost compare to the chosen industry.  This gives you the confidence to know where your estimate falls against comparable completed projects (of a given size.) If your estimates fall outside the bounds of a single standard deviation above or below the industry trend lines, you know that you may want to reassess the assumptions of your estimate.

Once you begin to collect the data from your own completed projects, the data can be loaded and formulate your own corporate trend line(s).  The more completed projects you amass, the better your own future estimates will be.  In the meantime, good, solid estimates can still be done using the power of SLIM.

So, don’t fret, PM, you can develop good estimates immediately – you simply need to accurately size your projects and evaluate your project characteristics.

- Carol

QSM hosts a free advice column for software professionals who seek help to solve project management, communication and general software project issues. Carol Dekkers is a QSM consultant and IT measurement and project management expert who speaks internationally on topics related to software development. Send your questions to Ask Carol!

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