EstimatingUsing Effort and

Duration

Project Management

Introduction to Estimation

• Estimating is argued to be one of the most difficult tasks in Project Scheduling• This is due to the lack of available specific data regarding product resources i.e.

how much a product will cost, how long it will take etc.• The lack of this data means that project managers can only provide estimates• These estimates are usually wide ranging• Wide ranging estimates are better than specific estimates which are likely to be

wrong

Estimating Project costs with Duration and Effort

• Before the start of a project three things must be estimated:

• Duration: time the project will take• Effort: the amount of work• Cost: how much the project will cost financially

Estimating Project Costs with Duration and Effort

• Effort must be estimated first• Duration can be estimated from the amount of effort required and

the resources which are available• Once effort and duration have been establish project costs can be

estimated using labour and non-labour items

Techniques for Estimating

• Quantitatively based or Parametric Estimating• Analogous Estimating or As-buts• Bottom-up Estimating • Using Learning Curve Effects• Wishful thinking• Expert judgement

Parametric Estimating

• Works best when there is existing experience of similar projects• Project is broken down into units which can then be estimated using independent

variables• These variables are often standard or previously known variables• Costs can be estimated from knowledge of what work is being undertaken• Relies on repetition in previous projects • Similar to Analogous estimating but follows a more statistical approach • The accuracy of the data/known variables effects the accuracy of this approach

Analogues Estimating or As….Buts• Useful for early project estimates• The organisation uses previous experience which is similar to make an estimate• Use costs from previous experience as a guideline for estimation• If previous projects are not reviewed then the accuracy of previous estimates is

unknown• Therefore previous costs etc. might not provide valuable valid estimates• This may cause mistakes to be repeated as no learning has occurred• Previous estimates can be used if they are reviewed and augmented

Bottom-up Estimating

• The project is broken down into estimated components• Each component is broken down further to allow for greater understanding• The costs of each work component is summed from the bottom up to provide an

estimation for the whole project.

Learning Curve Effects• There will be areas of repetition in projects, repetition decreases the time

required for tasks as they are known and learning has already occurred• Subsequent improvements in speed are seen to become smaller over time• This can be quantified using the following formula:

Yx = Kxn

where• x = the number of times the task has been carried out• Yx = time taken to carry out the task the xth time• K = time taken to carry out the task the first time• n = log b/log 2 where b = learning rate

Wishful Thinking

Some causes of wishful thinking occurring are:• Optimism Bias: being over-optimistic regarding timeframes and costs• Politics: for examples when objectives are regarded as being more

important than costs• Failure to be systematic about planning: i.e. people making estimates

can be complacent and/or unqualified

Expert Judgement

• Estimation requires a degree of expert judgement• There is a degree of expert judgement required in the project and of the business

area. • The project manager is assumed to have expert judgement

Problems with Estimates

• Inappropriate use of estimates: i.e. rough estimates may be used as definitive estimates. • Inappropriate data used to generate estimates: such as irrelevant past

experience• Estimates are taken out of context: for example initial estimates are

used when changes have been made to the project

Nature, Role and Accuracy of Estimate TypesName Nature Role Accuracy

Rough/Ballpark Much uncertainty as to what is involved

Early check on feasibility of brief

Very low

As-buts As was carried out previously but with some amendments

With an appropriate contingency factor, can be used for proposals

Moderate

Detailed Estimates Some initial work is carried out to determine what the likely problems are going to be

Proposals Moderate

To Finish Much of the Project is completed and additional funding is needed to complete the tasks

Additional fund requests High

Source: Maylor. 2010. Project Management

Parkinson’s Law

• An activity will expand to fill the time available • A critical review of Parkinson’s Law and it’s implications can be found

in the article belowGenaro J. Gutierrez and Panagiotis Kouvelis, Parkinson's Law and Its Implications for Project Management. Management Science. Vol. 37, No. 8 (Aug., 1991), pp. 990-1001

Techniques for Accuracy 1. Clarify the project priorities, understand the scope of the project2. Incorporate time to generate estimates in the project plan3. Break the project down into detailed tasks4. Use learning from previous projects5. Avoid making estimates to please management6. Refine the project scope throughout the duration of the project to

improve accuracy 7. Use multiple estimating techniques

Techniques for Accuracy

• Bottom up estimating and Parametric estimating offer the highest levels of accuracy • Bottom up estimating: provides the highest level of accuracy when

there is suitable detail regarding the components• Parametric Estimating: provides high levels of accuracy when the data

is of good quality and due to the statistical nature of the approach

Further Reading

• Maylor: Project Management, 4th ed, Chapter 6 & 8

• Chapman., and Ward. 2003. Constructively Simple Estimating: a Project Management Example. Journal of the Operation Research Society. 54. 1050-1058.

References

• Maylor, H., 2010. Project Management. 4th ed. Chester: Pearson

• Tom Mochal, 2006. Estimate project costs after you have estimated effort and duration. [Online] Available at: http://www.techrepublic.com/article/estimate-/project-costs-after-you-have-estimated-effort-and-duration/ [Accessed: 07/11/13]

• CHRIS O'HALLORAN, 2013. Project Estimation Techniques and Templates. [Online] Available at: http://strikingprojectmanagement.com/project-estimation/ [Accessed 07/11/13]

• Adele Sommers, 2013. 12 Tips for Accurate Project Estimating. [Online] Availbale at: http://www.projectsmart.co.uk/12-tips-for-accurate-project-estimating.html [Accessed 07/11/13]

• MindTools, 2013. Estimating Time Accurately. [Online] Available at: http://www.mindtools.com/pages/article/newPPM_01.htm [Accessed 07/11/13]