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Introduction to Estimating

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Assessments of the likely quantitative results of activities ... The number of labour units required to complete an activity. Usually expressed as staff ... – PowerPoint PPT presentation

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Title: Introduction to Estimating


1
Introduction to Estimating
  • Estimates, assumptions, duration and effort

2
Estimation exercise
  • Part I

3
What are estimates?
  • Assessments of the likely quantitative results
    of activities
  • Always based on assumptions
  • Used to predict effort and duration
  • Things that should always include some
    indication of
  • Accuracy or
  • Certainty
  • Things that should always be qualified
  • (e.g. preliminary, high-level, low-level)
  • NOT actuals

4
What are assumptions?
  • Factors that, for planning purposes, are
    considered to be
  • True
  • Real, or
  • Certain
  • Factors that affect all aspects of project
    planning
  • Identified, documented, and validated as part of
    the planning process
  • Part of the progressive elaboration of the
    project
  • Things that generally involve a degree of risk

5
Duration and effort whats the difference?
  • Duration is
  • The number of work periods required to complete
    an activity
  • Usually expressed as workdays or workweeks
  • Sometimes incorrectly equated with elapsed time

6
Duration and effort whats the difference?
  • Effort is
  • The number of labour units required to complete
    an activity
  • Usually expressed as staff hours, staff days or
    staff weeks
  • Should not be confused with duration, and padding
    should not be added

7
Estimation exercise
  • Part II

8
Approaches to estimating top down estimating
  • Also called analogous estimating
  • Uses the actual durations of a previous, similar
    activity as the basis for estimating the duration
    of a future activity
  • Frequently used to estimate when there is a
    limited amount of detailed information available
    (e.g. in the early stages of a project)
  • Requires expert judgment
  • Example Project A took 3 months to deliver,
    Project B is similar, therefore Project B will
    take 3 months to deliver

9
Approaches to estimating bottom up estimating
  • Estimating the effort required to complete
    specific tasks, then summarizing or rolling up
    the the individual estimates to come to a total
  • Generally considered to be more accurate than
    top-down estimating
  • Example Activity X is made up of 2 tasks task
    A and task B. Task A will take 3 hrs of effort,
    and task B will take 10 hrs of effort, therefore
    activity X will take 13 hrs of effort.

10
Estimation exercise
  • Part III

11
Estimation techniques quantity-based estimates
  • Also called parametric modeling
  • Quantities to be performed for each specific
    work category multiplied by the productivity unit
    rate
  • Quantity of Work Category Productivity
    Unit Rate Effort
  • 10 HTML pages 2 hrs per page 20
    hrs of effort
  • Useful even if the quantity for each work
    category is unknown assumptions can be made and
    estimates can be based on those

12
Estimation techniques the WAVE technique
  • Weighted AVErage calculates an average skewed
    towards the most likely estimate
  • Low (4 Most Likely) High Effort
  • 6
  • TTC to work
  • 20 mins (4 30 mins) 90 mins
    38.3 mins
  • 6
  • Generally considered to produce more accurate
    estimates

13
What is variance?
  • Any difference between the estimated cost of an
    activity and the actual cost
  • Any difference between the scheduled completion
    of an activity and the actual completion

14
Estimation exercise
  • Part IV

15
Estimation exercise
  • And the answer is
  • (to be revealed in workshop)

16
Review the tie back
  • Estimates are assessments of the likely
    quantitative results of activities
  • Estimates are based on assumptions
  • Estimates are used to predict effort and
    duration
  • Estimates should be revised as assumptions
    change
  • Estimates should always include a degree of
    accuracy or certainty
  • Estimates should always be qualified
  • Top-down estimates require expert judgment, and
    are typically inaccurate
  • Estimate early, estimate often!

17
Thank you!
  • For more information, please visit
  • http//importantprojects.co.uk
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