Ugly Duckling was asked to give a second opinion on the hour estimation of a large IT implementation project of a financial solution developed by team outside the IT landscape. We started by creating a large detailed list of each activity and sub-activity expected to be carried out during the project. The list contained an optimistic as well as a pessimistic estimate.
The optimistic approach consider that all the (sub-)activities are carried out smoothly with no unexpected delays and/or additional exceptional activities. In the pessimistic approach things go wrong and/or unexpected activities arise, i.e. project risks materialise. The pessimistic approach estimates the extra time to deal with these risks.
Based on the list it was easy for management to assess whether estimations were within realistic bounds and where further investigation was needed.