Some months ago I read an MSc in Computer Science thesis that can be very useful for your purpose: An Investigation of Team Effectiveness in Agile Software Development by Lars Martin Riiser Haraldsen. Its main objective is to investigate:
How does the Scrum methodology facilitate team effectiveness and what are the advantages and disadvantages?
The author defines team effectiveness as a:
[...] measure of a team working together in such a way that the core goals are accomplished within a certain time frame and the team members are satisfied.
The model adopted is based on this paper written by Salas, Sims, and Burke. According to these authors, the core components of teamwork include: team leadership, mutual performance monitoring, backup behavior, adaptability, and team orientation. All of these areas are needed to achieve good team effectiveness, but their implementation can be different from project to project.
I suggest you to give a look at Chapter 5 to see the author's findings in detail. From Chapter 6:
Overall, I have found that Scrum facilitates teamwork and will in most areas increase team effectiveness. [...] the studies also show that when using agile development, such as Scrum, and follow the guidelines correctly, teams are satisfied and productivity improves.