Learn about the Activity DurationEstimating (Tools and Techniques) in theCert IV Project Management qualification.
Expert Judgment. Activity durations are often difficult toestimate because of the number of factors that caninfluence them, such as resource levels or resourceproductivity. Expert judgment, guided by historicalinformation, can be used whenever possible.The individual project team members may also provideduration estimate information or recommended maximumactivity durations from prior similar projects. If suchexpertise is not available, the duration estimates are moreuncertain and risky.
Analogous Estimating. Analogous duration estimatingmeans using the actual duration of a previous, similarschedule activity as the basis for estimating the duration ofa future schedule activity. It is frequently used to estimateproject duration when there is a limited amount of detailedinformation about the project for example, in the earlyphases of a project.Analogous estimating uses historical information and expertjudgment. Analogous duration estimating is most reliablewhen the previous activities are similar in fact and not justin appearance, and the project team members preparingthe estimates have the needed expertise.
Parametric Estimating. Estimating the basis for activitydurations can be quantitatively determined by multiplyingthe quantity of work to be performed by the productivityrate. For example, productivity rates can be estimated on adesign project by the number of drawings multiplied bylabour hours per drawing, or a cable installation in metersof cable times labour hours per meter.The total resource quantities are multiplied by the labourhours per work period or the production capability per workperiod, and divided by the number of those resourcesbeing applied to determine activity duration in workperiods.
Three-Point Estimates. The accuracy of the activityduration estimate can be improved by considering theamount of risk in the original estimate. Three-point estimatesare based on determining three types of estimates:• Most likely. The duration of the schedule activity, given theresources likely to be assigned, their productivity, realisticexpectations of availability for the schedule activity,dependencies on other participants, and interruptions.• Optimistic. The activity duration is based on a best-casescenario of what is described in the most likely estimate.• Pessimistic. The activity duration is based on a worst-casescenario of what is described in the most likely estimate.
An activity duration estimate can be constructed byusing an average of the three estimated durations. Thataverage will often provide a more accurate activity durationestimate than the single point, most-likely estimate.
Reserve Analysis. Project teams can choose to incorporateadditional time referred to as contingency reserves, timereserves or buffers, into the overall project schedule asrecognition of schedule risk. The contingency reserve can bea percentage of the estimated activity duration, a fixednumber of work periods, or developed by quantitativeschedule risk analysis.The contingency reserve can be used completely or partially,or can later be reduced or eliminated, as more preciseinformation about the project becomes available. Suchcontingency reserve is documented along with other relateddata and assumptions.
There is a tendency to consume contingencies by default!Two academic theories that discuss this are:Parkinson’s Law – Work expands to fill the time available;Student Syndrome – People will start to fully applythemselves to a task at the last possible moment before adeadline.
Activity Duration Estimating: OutputsActivity Duration Estimates. Activity duration estimatesare quantitative assessments of the likely number of workperiods that will be required to complete a schedule activity.Activity duration estimates include some indication of therange of possible results. For example:• 2 weeks ± 2 days to indicate that the schedule activity willtake at least eight days and no more than twelve(assuming a five-day workweek).• 15 percent probability of exceeding three weeks to indicatea high probability-85 percent-that the schedule activity willtake three weeks or less.
Activity Attributes (Updates). The activity attributes areupdated to include the durations for each schedule activity,the assumptions made in developing the activity durationestimates, and any contingency reserves.LMIT’s Diploma in Project Management is NowEndorsed by AIPM – Get Your Diploma of PM and You’llAlso Receive a Certificate from AIPM.
LMIT provides online training courses forthe Cert IV Project ManagementBSB41507, the Certificate IV of ProjectManagement and the Diploma of ProjectManagement BSB51407 in Brisbane, Sydney,Melbourne, Perth, Adelaide and Canberra.