Sizing in an Agile context
Story Points are a metric used in agile project management and development to estimate the difficulty of implementing a given story. In this context, a story is a particular business need assigned to the software development team. Story Points are a relative measure of effort with respect to a simple story that is known to the whole team and defined as 1 Story Point. Story points sizes are assigned according to (an adaptation of) a Fibonacci sequence. Elements considered in assigning a story point size include the complexity of the story, the number of unknown factors and the potential effort required to implement it.
Assigning story point sizes to stories is usually done per iteration or sprint in a planning poker session. Each team member can assign a story point size by means of a planning poker card with a number from (an adaptation of) a Fibonacci sequence. During the discussion of a story, numbers must not be mentioned at all to avoid anchoring, where the first number spoken aloud sets a precedent for subsequent estimates. After discussion each team member assigns a size value by playing a card. When all team members play the same card, there is agreement about the size. When the numbers vary, the lowest and highest values are explained and discussed and a new round of cards is played.
This process is a variation of the Wideband Delphi method. It is commonly used in agile software development. The planning poker method was first defined and named by James Grenning in 2002.