Does Planning Poker work?
Absolutely! Teams estimating with Planning Poker consistently report that they arrive at more accurate estimates than with any technique they'd used before.
One reason Planning Poker leads to better estimates is because it brings together multiple expert opinions. Because these experts form a cross-functional team from all disciplines on a software project, they are better suited to the estimation task than anyone else.
After completing a thorough review of the literature on software estimation, Magne Jørgensen, Ph.D., of the Simula Research Lab concluded that “the people most competent in solving the task should estimate it.”
Second, a lively dialogue ensues during poker planning, and estimators are called upon by their peers to justify their estimates. Researchers have found that this improves estimate accuracy, especially on items with a lot of uncertainty as we find on most software projects.
Further, being asked to justify estimates has also been shown to result in estimates that better compensate for missing information. This is important on an agile project because the user stories being estimated are often intentionally vague.
Additionally, studies have shown that averaging individual estimates during agile estimating and planning leads to better results as do group discussions of estimates.