Project Estimating Tips

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Project Estimating Tip #1

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Don’t say you’re “90% confident” in an estimate unless you have a quantitatively-derived basis for saying so.

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Project Estimating Tip #2

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Avoid using artificially narrow ranges. Be sure the ranges you use in your estimates don’t overstate your confidence in your estimates.

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Project Estimating Tip #3

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If you are feeling pressure to make your ranges narrower, determine whether that pressure is coming from an external source or whether it might possibly be coming from yourself.

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Project Estimating Tip #4

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Be humble about your ability to accurately estimate project outcomes. About 75% of all projects fail to meet their cost and schedule goals.

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Project Estimating Tip #5

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The systemic error tendency for most organizations is not neutrally inaccurate estimates; it is underestimation. The first step toward improving estimates for most organizations is to make the estimates bigger.

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Project Estimating Tip #6

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Recognize a mismatch between a project’s business target and a project’s estimate for what it is: rare and valuable risk information that the project might not be successful. Take corrective action early, when it can do some good.

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Project Estimating Tip #7

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Most businesses value predictability more than flexibility. Be sure you understand which your business values the most.

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Project Estimating Tip #8

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Don’t confuse estimates with targets or commitments.

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Project Estimating Tip #9

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Even if the target is set in concrete, you can still estimate to support planning the best way to hit the target.

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Project Estimating Tip #10

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When you’re asked to provide an estimate, determine whether you’re supposed to be estimating or figuring out how to meet a target.

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Project Estimating Tip #11

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When you see a single-point “estimate,” ask whether the number is an estimate or whether it’s really a target.

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Project Estimating Tip #12

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All estimates are probability statements, explicitly or implicitly. When you see a single point estimate, that number’s probability is not 100%. Ask what the probability of that number is.

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Project Estimating Tip #13

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You can make a commitment to the optimistic end or the pessimistic end of an estimation range—or anywhere in the middle. The important thing is for you to know where on the range your commitment falls and to make conscious plans based on the level of risk that implies.

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Project Estimating Tip #14

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Aim for estimates that will be within about 20% of the project’s actual results. Ask whether better accuracy is really needed, or whether future changes in the project will invalidate the estimate’s assumptions anyway.

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Project Estimating Tip #15

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A good estimate is an estimate that gives the project manager a clear enough view of project reality to control the project to meet its targets.

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Project Estimating Tip #16

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Consider the effect of the Cone of Uncertainty on the accuracy of your estimate. Don’t pretend your estimate has more accuracy than is possible at your project’s current position within the Cone.

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Project Estimating Tip #17

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Don’t assume the Cone of Uncertainty will narrow itself. You have to do the work to remove sources of variability from your project and force the Cone to narrow.

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Project Estimating Tip #18

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Account for the Cone of Uncertainty in your estimates by using predefined uncertainty ranges.

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Project Estimating Tip #19

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Account for the Cone of Uncertainty in your estimates by having one person create the “how much” part of the estimate and a different person create the “how uncertain” part of the estimate.

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Project Estimating Tip #20

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Don’t expect better estimation practices by themselves to provide more accurate estimates for chaotic projects. You can’t accurately estimate an out-of-control process. Fix the chaos first, and then improve the estimates.

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Project Estimating Tip #21

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To deal with unstable requirements, consider project control strategies instead of or in addition to estimation strategies.

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Project Estimating Tip #22

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Include time in your estimates for stated requirements, implied requirements, and non-functional requirements—that is, all the requirements. Nothing can be built for free, and your estimate shouldn’t imply that it can.

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Project Estimating Tip #23

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Be sure you include all necessary software development activities in your estimates, not just coding and testing.

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Project Estimating Tip #24

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On projects that last longer than a few weeks, include allowances for overhead activities such as vacations, sick days, training days, company meetings, and so on.

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Project Estimating Tip #25

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Don’t reduce developer estimates—they’re probably too optimistic already.

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Project Estimating Tip #26

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Beware of subjectivity creeping into an estimate. The more times and places that subjectivity can creep in, the less accurate the estimate will tend to be.

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Project Estimating Tip #27

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Avoid having “control knobs” on your estimates. While control knobs might give you a feeling of better accuracy, they usually introduce subjectivity and degrade actual accuracy.

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Project Estimating Tip #28

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Don’t give off-the-cuff estimates. Provide 15-minute estimates instead.

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Project Estimating Tip #29

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Match the precision of your estimates to their accuracy.

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Project Estimating Tip #30

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Include allowances for project risk that are proportional to the level of project risk.

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Project Estimating Tip #31

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Invest an appropriate amount of effort assessing the size of the software that will be built. The size of the software is the single most significant contributor to project effort and schedule.

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Project Estimating Tip #32

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Don’t assume that effort scales up linearly as project size does. Effort scales up exponentially.

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Project Estimating Tip #33

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Use software estimation tools to compute the impact dis-economies of scale.

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Project Estimating Tip #34

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If you’ve completed previous projects that are about the same size as the project you’re estimating—defined as being within a factor of 3 from largest to smallest—you can probably safely use a ratio-based estimating approach such as lines of code per staff month to estimate your new project.

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Project Estimating Tip #35

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Consider the kind of software you develop in your estimate. The best way to account for the kind of software is by using historical productivity data from your own organization.

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Project Estimating Tip #36

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Because of the huge variations in individual performance, you can’t accurately estimate a small project or individual tasks within a larger project until you know who will do the work that’s being estimated.

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Project Estimating Tip #37

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When estimating a project, consider the experience of the programmers with the specific language and technology environment, the level of the language, the richness of the tool set, and whether the language is interpreted.

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Project Estimating Tip #38

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Use the COCOMO II adjustment factors to gain insight into your project’s strengths and weaknesses. For the actual estimates, use historical data instead.

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Project Estimating Tip #39

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Be sure your estimation approach accounts for the most significant influences on projects of the size you’re estimating. Influences change as project size changes.

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Project Estimating Tip #40

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Consider the project state, project size, development style, desired accuracy, cost of creating the estimate, and what you want to estimate when choosing an estimation approach.

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Project Estimating Tip #41

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Count if at all possible. Compute when you can’t count. Use judgment only as a last resort.

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Project Estimating Tip #42

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Look for something you can count that’s a meaningful measure of the scope of work in your environment.

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Project Estimating Tip #43

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Collect historical data that will support computing an estimate from a count.

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Project Estimating Tip #44

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Avoid tweaking estimates that have been derived through computation with expert judgment. Such “expert judgment” usually degrades an estimate’s accuracy.

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Project Estimating Tip #45

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Use historical data as the basis for estimate productivity assumptions.

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Project Estimating Tip #46

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Unlike mutual fund disclosures, your organization’s past performance really is your best indicator of future performance.

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Project Estimating Tip #47

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Use historical data to help avoid politically charged estimation discussions arising from assumptions like “my team is below average.”

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Project Estimating Tip #48

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In collecting historical data to use for estimation, start small and be sure you understand what you’re collecting.

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Project Estimating Tip #49

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Collect a project’s historical data contemporaneously if at all possible.

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Project Estimating Tip #50

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Collect historical data on a regular basis as a project is underway so that you can build a data-based profile of how your projects run.

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Project Estimating Tip #51

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The most valuable historical data you can collect is data from your current project.

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Project Estimating Tip #52

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Use historical data rather than industry average data to calibrate your estimates, if possible. In addition to making your estimates more accurate, historical data will reduce variability in your estimate arising from uncertainty in the productivity assumption.

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Project Estimating Tip #53

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If you don’t currently have historical data, begin collecting it as soon as possible.

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Project Estimating Tip #54

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Have the people who will actually do the work create the task-level estimates.

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Project Estimating Tip #55

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Create best case/worst case estimates to stimulate thinking about the full range of possible outcomes.

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Project Estimating Tip #56

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Use an estimation checklist to improve your individual estimates. Develop and maintain your own personal checklist to improve your estimation accuracy.

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Project Estimating Tip #57

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Collect personal data on estimated performance vs. actual performance so that you can improve your individual estimates over time.

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Project Estimating Tip #58

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Break large estimates into small pieces so that you can take advantage of the Law of Large Numbers—the high errors and low errors canceling each other out.

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Project Estimating Tip #59

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Break large estimates into at least five pieces—or as many as your phase in the project (and your tolerance for detail) will support.

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Project Estimating Tip #60

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Use a generic software-project WBS to avoid omitting the most common activities.

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Project Estimating Tip #61

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Use the simple standard deviation formula to compute meaningful rolled-up Best Case and Worst Case estimates when you have about 10 tasks or fewer.

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Project Estimating Tip #62

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Use the complicated standard deviation formula to compute meaningful rolled-up Best Case and Worst Case estimates when you have about 10 tasks or more.

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Project Estimating Tip #63

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Don’t divide by 6 to obtain tasks’ standard deviations. Choose a divisor based on the accuracy of your estimation ranges.

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Project Estimating Tip #64

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Focus on making your “expected case” estimates accurate. If the individual estimates are accurate, aggregation will not create problems. If the individual estimates are not accurate, aggregation will be problematic until you find a way to make them accurate.

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Project Estimating Tip #65

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Estimate new projects by comparing them to similar past projects.

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Project Estimating Tip #66

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Do not address estimation uncertainty by biasing the estimate. Address uncertainty by expressing the estimate in uncertain terms.

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Project Estimating Tip #67

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Use Fuzzy Logic to estimate program size.

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Project Estimating Tip #68

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Consider using Fuzzy Logic to estimate effort.

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Project Estimating Tip #69

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When using the results of a statistical calculation, remember to round the results before you present them to non-estimators.

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Project Estimating Tip #70

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Consider using Standard Components as a low effort technique in a project’s early stages.

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Project Estimating Tip #71

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Use Story Points in conjunction with iterative development to obtain an early estimate of a project’s schedule and effort that is based on data from the same project.

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Project Estimating Tip #72

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Exercise caution when calculating estimates that use numeric ratings scales. Be sure the numbers in the scale work the way you think they do. Avoid performing calculations on numbers that aren’t supported by the underlying ratios.

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Project Estimating Tip #73

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Use T-Shirt Sizing (i.e., small, medium, large, etc.) to help non-technical stakeholders rule features in or out in the wide part of the Cone of Uncertainty.

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Project Estimating Tip #74

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Count whatever makes the most sense in your environment, collect calibration data on that, and use that to create estimates that are well suited to your environment.

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Project Estimating Tip #75

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Use group reviews to improve estimation accuracy.

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Project Estimating Tip #76

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Use Wideband Delphi for early-in-the-project estimates, for unfamiliar systems, and when several diverse disciplines will be involved in the project itself.

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Project Estimating Tip #77

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Use an estimation software tool to sanity check estimates created by manual methods. Larger projects should rely more heavily on commercial estimation software.

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Project Estimating Tip #78

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Don’t treat the output of a software estimation tool as divine revelation. Sanity check estimation tool outputs just as you would sanity check estimates created using the art of estimation.

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Project Estimating Tip #79

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Use multiple estimation techniques, and look for convergence or spread among the results.

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Project Estimating Tip #80

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If different estimation techniques produce different results, try to find the factors that are making the results different. Continue re-estimating until the results converge to within about 5%.

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Project Estimating Tip #81

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If multiple estimates agree and the business target disagrees, trust the estimates.

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Project Estimating Tip #82

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Don’t debate the output of an estimate. Take the output as a given. Change the output only by changing the inputs and re-computing.

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Project Estimating Tip #83

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Focus on estimating size first. Then compute effort, schedule, cost, and features from the size estimate.

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Project Estimating Tip #84

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Re-estimate.

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Project Estimating Tip #85

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Change from less accurate to more accurate estimation approaches as you work your way through a project.

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Project Estimating Tip #86

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When you are ready to hand out specific development task assignments, you’re ready to switch to bottom-up estimation.

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Project Estimating Tip #87

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When you re-estimate in response to a missed deadline, base the new estimate on the project’s actual results, not on the project’s planned results.

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Project Estimating Tip #88

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Present your estimates in a way that allows you to tighten up your estimates as you move further into the project.

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Project Estimating Tip #89

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Communicate your plan to re-estimate to other project stakeholders in advance.

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Project Estimating Tip #90

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Review your projects’ estimation histories to assess the accuracy of your estimates and estimate ranges.