Strict Predictability of Cost and Schedule

If you need predictability about cost and schedule with an exact, fixed feature set, predictability comes into play after the exact feature set has been defined—which is usually 10–30% of the way into a release cycle.

These key Agile practices support strict predictability:

• Story point assignment

• Velocity computation

• Small stories

• Up-front population, estimation, and refinement of the product backlog

• Short iterations

• Release burndown

• Accounting for variability in velocity

If you don’t need strict predictability of cost and schedule, you might skip ahead to the next lesson, “Strict Predictability of Feature Set.” However, some of the concepts in this lesson are referenced in later lessons, so you might at least skim the headings before moving on.

Predictability support: Story point assignment

Direct estimation of effort is subject to issues of both bias and subjectivity (McConnell 2006). Bias is the intentional adjustment of the estimation in the desired direction. Subjectivity is the unintentional adjustment of the estimate due to wishful thinking or insufficient skill in estimation. The history of software development is that estimation is nearly always on the optimistic side, leading to a systemic tendency for individuals and teams to underestimate.

Story points are useful in part because they are not subject to bias. Instead of estimating effort directly, teams use story points to assign relative sizes to work items. People will often have a conversion factor in mind from hours to story points when they assign story points, but errors in those conversion ...