CSC/ECE 517 Fall 2010/ch6 6c VP

Size estimation in agile projects

Agile process separates estimation of size from estimation of duration. Initially, estimation of size is done and it is followed by estimation of duration. Both these estimations are done at 'user story' level.

size estimation

The size of a particular user story is determined after considering all the activities that are needed to be done to complete that user story. These activities include all the phases like Envision, Speculate, Explore and Adapt.When the user story is completed, one can assume that a part of the feature to the customer is completed. As with any estimation technique, size estimates has certain units which are as follows:

Estimation units

1. Story point - Story point is a random measure used by team to rate each user story and they are actually of no physical significance. This unit signifies the efforts required to complete the user story. As its unit do not give any significant meaning sometimes it is referred as bucks or points. This point system is a relative scale. It has no effect of any variance in time or team size and hence this unit is consistent among different person and time. After few estimations when team gets stable story points, estimation of further user stories becomes fast and easy.

2. ideal time - This is absolute scale to measure estimation. The ideal time is the actual time needed to complete a user story in an ideal case i.e., without considering any interrupts. Generally ideal time gets calculated in days or hours. It is practically observed that the actual elapse time is greater than the ideal time. Due to its absolute nature is it easy to understand this measure for person outside the team but meaning of ideal time may vary from person to person.

velocity estimation

estimation of delivery capability of the team is known as velocity. velocity helps to determine scope of each iteration and total project duration. total story points divided by velocity gives number of iterations need to complete the project. iteration length is fixed hence total duration of the project can be calculated by multiplying iteration duration by number of iterations to complete all user stories defined in a project.

Estimation unit

The velocity is measured in time mostly in number of days or hours.