3 pm3 t_2%20-%20activity%20duration%20estimating
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3 pm3 t_2%20-%20activity%20duration%20estimating 3 pm3 t_2%20-%20activity%20duration%20estimating Presentation Transcript

  • Activity Definition
    Activity List
    Resource Plan
    Activity sequencing
    Activity Resource
    Activity Duration
    Duration Estimate
    Network Diagram
    Integrated Schedule
  • Activity Duration Estimating
    Activity durations are the “calendar” time required to perform the work
    Duration comprises:
    Time spent by the resources actually performing the work
    Queue, wait or other inactive times
    Other times required before the effort is complete (eg. Paint cure times, automated test run times)
  • Duration Estimating Techniques
    Expert judgment
  • Expert Judgment
    Usually performed “bottom up”, often in conjunction with cost estimates performed as part of the proposal process
    Performed by “experts”:
    Functional “leads”/managers
    Project Management Staff
    Buy-in from performing staff and/or management
    Detailed treatment
    Can be overly optimistic/pessimistic depending on estimator bias
    Tendency to “build in” slack time
  • Analogous Estimating
    Usually performed, “Top down” - a form of expert judgment that uses information from previous similar estimates to generate duration estimates
    Usually performed by experienced project manager, manager, marketing person
    Property X is a 6 story building which took 6 weeks to erect; property Y is a similar type of building with same foundation footprint and utilities, but 3 stories tall – estimate it takes 3 weeks to erect
    Quick, inexpensive estimate that can be performed before product team is assigned
    Can be applied to even relatively poorly defined activities
    Only useful when projects are similar in fact, not just in appearance (eg. Property X built in Toronto, Property Y built in Greenland)
    Difficult to apply to lower level tasks
  • Parametric Estimating
    Used for repetitive tasks where metrics are maintained
    Number of engineering drawings
    Square feet of construction
    Lines of programming code
    SW Coding=4 hours/line of code
    Quick and easy to use
    Can draw on “Industry standard” handbooks which base estimates on broad data sets (eg. Construction estimating guides)
    Most project work does not fall into this category
    Only applicable where large data sets are available, yielding relevant averages
  • Example: SW Lines of Code
    Estimated Development Effort:
    (Basic COCOMO model, Person-Months = 2.4 * (KSLOC**1.05))
    Estimated Schedule:
    (Basic COCOMO model, Months = 2.5 * (person-months**0.38))
  • Probabilistic Estimating
    The methods so far produce “Deterministic” estimates
    Useful if the duration is known with a fair amount of certainty (eg. Time to produce a test report)
    For most estimates, the duration is uncertain
    (eg. Time to run the test: what if it fails? No equipment? Equipment fails? Etc.)
    in this case, need some way to account for the “probability” of things going better or worse than planned
    Two methods of accounting for uncertainty:
    Weighted average estimate
    Three point estimate used in schedule risk simulation
  • Weighted Average Estimates
    Probability follows a distribution (eg. For most naturally occuring phenomena = the “normal distribution or “bell curve”)
    Activity durations do not typically follow a “normal” distribution
    left skewed – ie. The difference between the soonest completion and the most likely completion date is smaller than between the mostly likely date and the latest completion
    early studies by US DoD lead to adoption of a “triangular distribution” called the “PERT distribution” because it was used in the “Program Evaluation and Review Technique” concurrently developed
    A single point estimate for a PERT distributed task is
    Where to , tm , and tp are the optimistic, “most likely” and pessimistic estimates
    Example: a test usually takes 2 days to set up and run; if setup goes smoother than usual it takes 1 day; if the test equipment breaks down and needs maintenance, it takes 5 days for this, and the initial 2 days for set up and running = 7 days
    to tm tp
    to +4 tm + tp
    1 +4x2 + 7
    to tm tp
    Estimated duration = = 2.4 days
  • Schedule Risk Modelling
    Statistical techniques used to “model” entire schedule based on multiple duration estimates for each task
    Eg. Monte Carlo analysis
    to , tm , and tp are input into a random number generator which produces an estimated time for each task
    Sample total schedule duration is calculated by applying sequence logic
    Process is iterated until a “steady” distribution of final durations is modelled
  • Adding Schedule Duration
    Entering into the Activity List
    Entering into the “Task Info” box
  • Schedule “Leads” and “Lags”
    Technique that introduces a time delay to a sequencing relationship to add realistic timing without unnecessary tasks
    Eg. Allow time for the customer to approve test results
    add a lag = 36FS+4d, the phone call will now happen 1d after the paperwork starts
    Must exercise caution not to replace actual work with a lag (eg. Time between work completion and shipment may include test, inspect, paperwork – these should be tasks)
  • Typical Activity Duration Estimating Procedure
    During proposal phase, the proposal manager and/or project manager produces a high level schedule based on an analagous estimate
    During the preliminary planning phase, detailed activity duration estimates are developed by team leads using expert knowledge and parametric estimating where possible
    Upon review of the preliminary schedule, critical and near-critical paths may be subjected to risk modelling to identify areas for mitigation planning, and possible schedule reserve allowances
    During project execution, team leads revise duration estimates using expert knowledge modified by analagous estimating drawn from project experience to date