Starting in 2012, Google’s People Operations began to investigating what makes teams effective. The result, after two years of research and hundreds of case studies, was the following:
Who is on a team matters less than how the team members interact, structure their work, and view their contributions. 
They identified five critical dynamics that, at Google, set apart successful teams: psychological safety, dependability, structure and clarity, the meaning of work, and impact of work.
Out of this, the most impactful dynamic was the first, team psychological safety. In 1999 Amy Edmonson defined team psychological safety as
[...] a shared belief that the team is safe for interpersonal risk taking. 
An improvement in psychological safety might be needed if, in your team, people fear asking for help or do not feel entitled to leave constructive feedback or report difficulty in contributing ideas because they might be different or considered “silly.”
To investigate this and the other four dynamics, at Intelligent Hack, we advise running a periodic health check based asking teams how much they agree with these statements:
- “If I make a mistake on our team, it is not held against me.”
- “When my teammates say they’ll do something, they follow through with it.”
- “Our team has an effective decision-making process.”
- “The work I do for our team is meaningful to me.”
- “I understand how our team’s work contributes to the organization’s goals.”
Running this survey periodically and consistently allows statistical analysis and identification of critical areas that need improvement. With the correct interpretation and guidance, such a tool is an invaluable objective measure of team health and a predictor of team effectiveness.
What if your team needs to improve their psychological safety or some other key indicator? Amy Edmondson proposes three bits of advice: 
- Frame the work as a learning problem, not an execution problem.
- Acknowledge your own fallibility.
- Model curiosity and ask lots of questions
Another technique we at Intelligent Hack use is to frame the team using the Five dysfunctions of a team framework and with a servant leadership approach. This allows us to work with the team with conventional methods and gives us a little more predictability of the outcome.
We can find more insight in the ample literature available on the subject. We can advise these two articles in addition to the resources linked:
- Evidence for a Collective Intelligence Factor in the Performance of Human Groups, Anita Williams Woolley, et al., Science, 2010
- The 2019 People Management Report
In conclusion, it has been scientifically proven that teams need a certain level of psychological safety to be productive. It is advisable to constantly monitor this indicator because a lack of security certainly requires management intervention. When an intervention is needed, be careful to use reliable methods, like servant leadership, to ensure lasting results.
: https://rework.withgoogle.com/blog/five-keys-to-a-successful-google-team/ “The five keys to a successful Google team, Julia Rozovsky, Google’s People Operations, 17/11/2015”
: https://www.jstor.org/stable/2666999 “Psychological Safety and Learning Behavior in Work Teams, Amy Edmondson, Administrative Science Quarterly, 6/1999”
: https://www.youtube.com/watch?v=LhoLuui9gX8 “Building a psychologically safe workplace, Amy Edmondson, TEDxHGSE, 5/5/2014”