Out of several estimation techniques involved in Scrum, few are noted below.
1- Wideband Delphi
2- Relative sizing / Story Points.
3- Affinity Estimation.
4- Estimate Range.
Wideband Delphi is a group-based estimation technique for determining how much work is involved and how long it will take to complete. Individuals within a team anonymously provide estimation for each feature, and the initial estimates are plotted on a chart. The team then discusses the factors that influenced their estimates and proceed to a second round of estimation. This process is repeated until the estimates of individuals are close to each other and a consensus for the final estimate can be reached.
Planning poker is one example of a Wideband Delphi technique. It is also important to note that it is the individual input collected by a mechanism that avoids the group thinking. Then the individual inputs are used for a group decision.
Relative Sizing / Story Points.
In addition to being used for estimation cost, story points can also be used for estimating the overall size of a User Story or feature. This approach assigns a story point value based on an overall assessment of the size of a User Story with consideration given to risk, amount of effort required, and level of complexity. This assessment will be conducted by the Scrum Team and a story point value will be assigned. Once an evaluation is done on one User Story in the Prioritized Product Backlog, the Scrum Team can then evaluate other User Stories relative to that first story. For example, a feature with a 2-point story value must be twice as difficult to complete as a feature with a 1-point story; a 3-point story should be three times as difficult to complete as a 1-point story.
Affinity estimation is a technique used to quickly estimate a large number of User Stories. Using sticky notes or index cards or tape, the team places User Storied on a wall or other surface, in order from small to large. For this, each team member begins with a subset or User Stories from the overall Prioritized Product Backlog to place by relative size. This initial placement is done in silence. Once everyone has placed their User Stories on the wall, the team reviews all the placements and may move User Stories around as appropriate. The second part of the exercise involves discussion. Finally, the Product Owner will indicate some sizing categories on the wall. These categories can be small, medium or large, or they may be numbered using story point values to indicate relative size. The team will then move User Stories into these categories as the final step in the process. Some key benefits of this approach are that the process is very transparent, visible to everyone, and is easy to conduct.
Estimates for projects should be presented in ranges. Precise figures may give an impression of being highly accurate when in fact they may not be. In fact, estimates by definition are understood not to be precisely accurate. Estimate ranges should be based on the level of confidence the team has in each estimate. The range can be narrow when the team is confident and wide when the team is less confident.