Written by Reedy Feggins, IBM
RTC 3.0 uses three different attributes to help teams determine which work items should be done during the sprint / iteration. These attributes are: Priority, Ranking and Complexity which are covered in detail in the article Customizing the Agile Planning tools in Rational Team Concert 2.0 provides a thorough discussion of the topic with screenshots from RTC 2.x but still remains valid in the RTC 3.x release.
Can you provide some guidance on the relative ranking when assigning this to stories?
The Level of effort estimate is captured using the complexity attribute for Stories where the Story Points are often used. In some implementations Epics don’t have a complexity attribute while level of effort estimate for a Task is almost always captured in Hours, see figure below.
By default RTC complexity ranking for the Story work item uses Story Points. In Agile, a Story Point is a unit less measure of time that teams use to estimate to estimate the work that the team will commit to in a sprint. Story points are NOT meant to be directly mapped to calendar time (days/hours) for estimation but instead are mean to help teams create better estimates, often using relative estimating techniques called Poker planning.
What is the default to be used for the complexity ranking? We have 1,2,3,5,8,13, 20, and 40,100. Is it recommended to modify this?
Estimates using story points mean that if you estimate two stories; one story was estimated as a one and the other story as a value of five, then the second story is 5 times bigger than the first. If a third story is estimated as a ten then it is 10 times bigger than the value of one. Why? so that when you know your team’s velocity equals 10 and you select a 1,2,3 and 5 point story for a sprint, you know they actually add up to a sum velocity of 10.
Studies have found that most people can estimate smaller numbers better but as the number become larger people estimates become less and less accurate so the larger the estimate, the larger the error.
We should give the scrum master some guidance on this relative ranking.
While some teams use a doubling sequence (1,2,4,8…), most Agile teams start off with Story estimates based on the Fibonacci sequence (1,2,3,5,8,13…), which is the default RTC complexity attribute. This mathematical sequence is used for relative ranking. In this approach when estimating, teams are not allowed to pick a number that doesn’t exist in the sequence.
 APA: Agile Commentary: Create a Proper Estimate Scale… (n.d.). Retrieved 02-20-2011 from http://agile-commentary.blogspot.com/2009/02/create-proper-estimate-scale.html