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


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

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