Estimating Process - High Level Estimates
With a Work Breakdown Structure (WBS) it is possible to do a high level estimate. The purpose of a high level estimate is to provide an estimate which will allow decision makers an opportunity to know how large of an effort (thereby the cost) will be do to the project.
High level estimates are based on relative sizing between the WBS items (requirements, use cases, deliverables, tasks, etc). The team will be grouping these items into the size categories of small, medium, large, and huge. These categories are relative to each other and are going to be very context dependent. The context is not only dependent the company, department, or industry but most importantly on the project team's view of each.
Using the spreadsheet I provide the WBS Identifier, Requirements Description and Tasks are available on the WBS worksheet. All that is required is to copy the estimation rows for the number of WBS Items that require estimation.
Set up a meeting where the team will sit down and come to consensus on each WBS Item as to its relative size. This will initially be very difficult because most people want to spend time defining what each relative size is.
It might be necessary to suggest an example to get past this step. If the team is very literal and detailed oriented then before the meeting bring in a large number of books (30 to 50) of different sizes. Then tell the team they have to sort the books into three piles, small, medium and large. Give them 3 minutes to do the effort and stop the them when the time is up.
After the exercise the team should be able to do relative size estimating fairly quickly. Make sure that the relative size estimates are based on a a consensus from the whole team.
The next effort has to do with the Feature Size Matrix and assigning Effort to each of the Use Case Size categories. Again a good idea to continue the book example. Have the team select one or two books that represent the average size of all the books for each of the three piles. Then have them estimate the number of pages that book has without looking inside the book. That number would the be the average book size for each pile.
Using the same method the team should look at all of the items which are in each of the Use Case Size categories and select one or two to do an estimate on how much effort will be needed to complete the selected work breakdown items. The effort becomes the Effort (person hours) for that particular Use Case Size. By entering the number into the Effort (person hours) every work breakdown item will then use that number.
When this effort is completed the high level estimate is completed and can be adjusted based on how early the estimate was performed. If you are providing a Rough Order of Magnitude (ROM) estimate then the worst case estimate is 10x (order of magnitude) the base estimate. This may seem excessive but remember what an order of magnitude means.
At this point the estimates should be presented to management for a decision as to whether or not the project should proceed.
Next article will be on a detailed estimate and using 3 point estimation techniques.