Estimate activity duration is an important project management process that helps you develop the project schedule. The accuracy of it depends on this process.
You use four tools to find the duration of your project or activities. The accuracy depends on when you do the estimation and the availability of the information.
As a project manager, you will use these techniques to provide duration estimates to your superiors. Understanding these terms is necessary.
Each activity has three attributes: resources required, the effort required and duration.
These attributes depend on each other. The more resources, the faster an activity can be completed. Moreover, an expert team member will take less time to complete a task than a novice team member. Therefore, first, apply the resources and effort. Then you will calculate the activity duration.
Estimate Activity Duration Tools
The following are four tools to estimate activity duration:
- Analogous Estimating
- Parametric Estimating
- Three Points Estimating
- Bottom-up Estimating
You can use this technique on a project level or an activity level for a quick result.
Analogous estimates use analogies from past similar projects. For example, assume you have to estimate the duration of a project, so you will look into your organizational process assets (OPA) for a similar completed project. You will then pick the project that resembles yours the most. Using your expert judgment, you will choose the duration estimate for your current project.
This technique is useful when you have little information about your project, and management needs quick answers. The accuracy of this estimation depends on the similarities between your project and the project you are comparing it to.
This technique is also known as “Top-down Estimation.”
- It is the fastest technique.
- This technique does not provide an accurate estimation.
- You can use this with a few project details.
This technique uses historical records to compute the duration estimate. Parametric estimation seems similar to analogous estimation but it has a very different approach.
This uses statistical, historical data to find the estimate. For example, if constructing a ten-foot wall took one day, then how long will it take to build a hundred-foot wall? Multiply the time taken to build a ten-foot wall by ten.
Or, if one room took three days to paint in an earlier project. How much time it will take to paint twenty rooms on your current project? You will multiply the time taken to paint one room on the old project by twenty to get the duration for your new project.
This technique is more accurate than the analogous estimation.
- It uses statistical relationships between historical data and variables.
- It is more accurate than the analogous technique.
Three Points Estimates
You can reduce bias using three-point estimates.
Triangular and beta distribution formulas are the most popular three-point estimates.
In three-point estimates, we use three parameters:
- Most Likely (Tm): This is the activity duration for most cases.
- Optimistic (To): This is the activity duration in the most favorable case.
- Pessimistic (Tp): This is the activity duration in the worst-case scenario.
The triangular estimate formula is:
Te = (To + Tm + Tp) / 3
PERT (Program Evaluation and Review Technique) is the most widely used three-point estimate technique.
It is a weighted average. The PERT estimate formula is:
Te = (To + 4Tm + Tp) / 6
Using a three-point estimate reduces the chance of risks, biased judgment, and uncertainty.
- It uses three estimates to calculate the average value of an activity’s duration.
- It reduces bias, risks, and uncertainties from the duration calculation.
- It is more accurate than analogous and parametric estimation.
Here, you will calculate the activities’ duration with the highest level of precision and add them together to get your project duration.
This is the most accurate, most time-consuming, and the most costly technique. It is also known as a “definitive estimate.”
- This is the most accurate technique and provides reliable results.
- You can use this technique when you have many details.
- This is a costly and time-consuming technique.
Knowing accurate activity durations helps you create a realistic schedule and helps you complete the project with minimal obstruction. Activity duration is an iterative process. You can repeat this process throughout the project life cycle as needed. It helps you establish the schedule baseline of the project.
This is an important process for your project’s success. Any deviation from the schedule baseline can affect your cost baseline. This is bad for your project and can damage the credibility of your organization.
This is an important topic from a PMP exam point of view. You will a few questions from this topic in your PMP exam.