Planning poker, also called Scrum poker, is a consensus-based technique for estimating,
mostly used to estimate effort or relative size of development goals in software development.
In planning poker, members of the group make estimates by playing numbered cards face-down
to the table, instead of speaking them aloud. The cards are revealed, and the estimates
are then discussed. By hiding the figures in this way, the group can avoid the cognitive
bias of anchoring, where the first number spoken aloud sets a precedent for subsequent
estimates. Planning poker is a variation of the Wideband
Delphi method. It is most commonly used in agile software development, in particular
the Scrum and Extreme Programming methodologies. The method was first defined and named by
James Grenning in 2002 and later popularized by Mike Cohn in the book Agile Estimating
and Planning, whose company trade marked the term.
Process The reason
The reason to use Planning poker is to avoid the influence of the other participants. If
a number is spoken, it can sound like a suggestion and influence the other participants' sizing.
Planning poker should force people to think independently and propose their numbers simultaneously.
This is accomplished by requiring that all participants show their card at the same time.
Equipment Planning poker is based on a list of features
to be delivered, several copies of a deck of cards and optionally, an egg timer that
can be used to limit time spent in discussion of each item.
The feature list, often a list of user stories, describes some software that needs to be developed.
The cards in the deck have numbers on them. A typical deck has cards showing the Fibonacci
sequence including a zero: 0, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89; other decks use similar
progressions.
The reason for using the Fibonacci sequence is to reflect the inherent uncertainty in
estimating larger items. Several commercially available decks use the
sequence: 0, ½, 1, 2, 3, 5, 8, 13, 20, 40, 100, and optionally a ? and a coffee cup.
Some organizations use standard playing cards of Ace, 2, 3, 5, 8 and King. Where King means:
"this item is too big or too complicated to estimate." "Throwing a King" ends discussion
of the item for the current sprint. Smartphones allow developers to use apps instead
of physical card decks. When teams are not in the same geographical locations, collaborative
software can be used as replacement for physical cards.
Procedure At the estimation meeting, each estimator
is given one deck of the cards. All decks have identical sets of cards in them.
The meeting proceeds as follows: A Moderator, who will not play, chairs the
meeting. The Product Manager provides a short overview.
The team is given an opportunity to ask questions and discuss to clarify assumptions and risks.
A summary of the discussion is recorded by the Project Manager.
Each individual lays a card face down representing their estimate. Units used vary - they can
be days duration, ideal days or story points. During discussion, numbers must not be mentioned
at all in relation to feature size to avoid anchoring.
Everyone calls their cards simultaneously by turning them over.
People with high estimates and low estimates are given a soap box to offer their justification
for their estimate and then discussion continues. Repeat the estimation process until a consensus
is reached. The developer who was likely to own the deliverable has a large portion of
the "consensus vote", although the Moderator can negotiate the consensus.
To ensure that discussion is structured; the Moderator or the Project Manager may at any
point turn over the egg timer and when it runs out all discussion must cease and another
round of poker is played. The structure in the conversation is re-introduced by the soap
boxes. The cards are numbered as they are to account
for the fact that the longer an estimate is, the more uncertainty it contains. Thus, if
a developer wants to play a 6 he is forced to reconsider and either work through that
some of the perceived uncertainty does not exist and play a 5, or accept a conservative
estimate accounting for the uncertainty and play an 8.
Benefits A study by Moløkken-Østvold and Haugen found
that [the] set of control tasks in the same project, estimated by individual experts,
achieved similar estimation accuracy as the planning poker tasks. However, for both planning
poker and the control group, measures of the median estimation bias indicated that both
groups had unbiased estimates, as the typical estimated task was perfectly on target.
References