Learn about the Activity Duration Estimating (Tools and Techniques) in the Cert IV Project Management qualification.
Expert Judgment. Activity durations are often difficult to estimate because of the number of factors that can influence them, such as resource levels or resource productivity. Expert judgment, guided by historical information, can be used whenever possible. The individual project team members may also provide duration estimate information or recommended maximum activity durations from prior similar projects. If such expertise is not available, the duration estimates are more uncertain and risky.
Analogous Estimating. Analogous duration estimating means using the actual duration of a previous, similar schedule activity as the basis for estimating the duration of a future schedule activity. It is frequently used to estimate project duration when there is a limited amount of detailed information about the project for example, in the early phases of a project.
Analogous estimating uses historical information and expert judgment. Analogous duration estimating is most reliable when the previous activities are similar in fact and not just in appearance, and the project team members preparing the estimates have the needed expertise.
Parametric Estimating. Estimating the basis for activity durations can be quantitatively determined by multiplying the quantity of work to be performed by the productivity rate. For example, productivity rates can be estimated on a design project by the number of drawings multiplied by labour hours per drawing, or a cable installation in meters of cable times labour hours per meter. The total resource quantities are multiplied by the labour hours per work period or the production capability per work period, and divided by the number of those resources being applied to determine activity duration in work periods.
Three-Point Estimates. The accuracy of the activity duration estimate can be improved by considering the amount of risk in the original estimate. Three-point estimates are based on determining three types of estimates:
- Most likely. The duration of the schedule activity, given the resources likely to be assigned, their productivity, realistic expectations of availability for the schedule activity, dependencies on other participants, and interruptions.
- Optimistic. The activity duration is based on a best-case scenario of what is described in the most likely estimate.
- Pessimistic. The activity duration is based on a worst-case scenario of what is described in the most likely estimate.
An activity duration estimate can be constructed by using an average of the three estimated durations. That average will often provide a more accurate activity duration estimate than the single point, most-likely estimate.
Reserve Analysis. Project teams can choose to incorporate additional time referred to as contingency reserves, time reserves or buffers, into the overall project schedule as recognition of schedule risk. The contingency reserve can be a percentage of the estimated activity duration, a fixed number of work periods, or developed by quantitative schedule risk analysis.
The contingency reserve can be used completely or partially, or can later be reduced or eliminated, as more precise information about the project becomes available. Such contingency reserve is documented along with other related data 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; and
Student Syndrome – People will start to fully apply themselves to a task at the last possible moment before a deadline.
Activity Duration Estimating: Outputs
Activity Duration Estimates. Activity duration estimates are quantitative assessments of the likely number of work periods that will be required to complete a schedule activity. Activity duration estimates include some indication of the range of possible results. For example:
- 2 weeks ± 2 days to indicate that the schedule activity will take at least eight days and no more than twelve (assuming a five-day workweek).
- 15 percent probability of exceeding three weeks to indicate a high probability-85 percent-that the schedule activity will take three weeks or less.
Activity Attributes (Updates). The activity attributes are updated to include the durations for each schedule activity, the assumptions made in developing the activity duration estimates, and any contingency reserves.
LMIT provides online training courses for the Cert IV Project Management BSB41507, the Certificate IV of Project Management and the Diploma of Project Management BSB51407 in Brisbane, Sydney, Melbourne, Perth, Adelaide and Canberra.
Published by: LMIT