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The Importance of Accurate Estimating

Document Info.

First Published
SM&P Issue 7

Reference Category
Estimating and Risk

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Reference

by: Charles Symons

The more accurate your estimate, the greater your ability to deliver on time and budget and satisfy your customers.

Few people realise that the most accurate estimate will also lead to the lowest cost development. There is no practical proof of this assertion, but the notion was first put forward by Abdel Hamid and Madnik ten years ago (Sloan Management Review, Fall 1990).

Their premise is (see illustration): if you over-estimate the effort and time that will be needed compared with what should be needed, then Parkinson's Law will apply. 'Work will fill the time made available for its completion.' On the other hand, if you under-estimate, this will only be discovered late in the life of the project, when you will either have to de-scope or add in extra resources to deliver the system on time. So over- or under-estimating leads to a higher cost than the most accurate estimate.

Other powerful arguments appeared in a paper by Fred Bootsma of Nortel at the 1999 IFPUG Annual Conference.

He reported the improvements in estimating accuracy he achieved by using the Full Function Points V1 method (a forerunner of COSMIC FFP) for estimating effort and schedule for telecommunications software. The side-benefits of improved estimating accuracy were felt at the organisation level and included:

improved scheduling of work and utilisation of resources
more reliable and faster delivery of product to the market-place.

The difficulty with accurate estimating is greatest early in the life of a project when you have the least knowledge of the requirements. There is always the danger that the estimator gets stuck with the early estimate because it has entered the sponsor's mind. It then becomes politically impossible to amend it later. Inaccurate estimating with un-stated uncertainty, giving a false impression of accuracy, is a recipe for disaster.

SMS training emphasises the importance of:

using multiple estimating techniques
making estimates as accurate as possible, quoting plus/minus ranges to allow for uncertainty
continuous estimating, providing updates as more information is obtained.

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Services

Estimating

Early Estimation
Estimating software size from the feasability stage through to early requirements gathering. Also approppriate for otuline designs.

Estimating Size
Estimating Size from detailed requirements and detailed designs.

Estimating Cost, Duration, Effort, etc
Developing estimates of cost etc from measurements or estimates of size in combination with other constraints.

Measuring Requirements and Changes
Measuring the functional size of change requests and estimating their impact in terms of cost, duration, effort etc.

Estimating Workshop
A group exercise conducted by a facilitator to produce a set of estimates.

Managing Risk

Managing Risk (Analysis and Amelioration)
Early preventative action could mean the difference between success and failure of every project. The job is not done until all identified threats have been managed in some way.

Risk Management Workshop
A group exercise to find and analyse probable project risks then develop strategies to ameliorate them.

Training

Estimating

Early Estimating of Software Size
A systematic & repeatable way to estimate using the partial information available during the first days of a project

Practical Estimating for Software Projects
Predict and control the effort, team size, schedule and cost of your software projects using proven methods

Estimating for Projects based on Use-Cases and the IBM/Rational Unified Process
Determine use-case size, effort, schedule and cost so your team can negotiate the cost/benefit landscape and agree development priorities with stakeholders

Estimating in Internet Time/Estimating for Web Developments
Extremely rapid development cycles necessitate just-in-time estimating to minimise risk and to assure incremental delivery runs smoothly

Managing Risk

Risk Analysis Workshop
Use this team workshop at any time during a project to identify threats to your project and agree what to do to ensure success

Managing Project Risk
Learn a systematic, repeatable approach that ensures teams identify, monitor and mitigate the threats to successful delivery of stakeholder requirements

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