Found this research about teams, although I'm not sure who performed the research.
The fastest teams have these qualities.
Dedicated: Everyone is on one and only one team.
Small: Fastest teams average 4.6 people (4 or 5 people).
Stable: Teams stay together for years.
Co-located: Team sits within touching distance all day.
Cross-functional: Each team member trained in 3 or more skills; this contributes to swarming.
Swarming: Team works one user story until it's done.
Protected: Team is not interrupted during sprint.
The conclusion? Launching great scrum teams is a scientific and repeatable process.