Most studies in this area show correlations, things like corporate boards with more women on them do better. Yes, there are obvious limitations to such studies.

Most studies in this area show correlations, things like corporate boards with more women on them do better. Yes, there are obvious limitations to such studies. Overall, we can probably safely say that 1. Too little diversity can be bad. For example, if you are making a product or a TV show that wants to reach as many people as possible, you should be aware of what those people would most want, and having your designers encompass those groups can help there. 2. Too much diversity can be bad. If your team all have different native languages then communication can be slower; if your team has extremely varied opinions on what you should be doing, you'll have many arguments; etc. Overall, an effective team needs focus and unity, and shared backgrounds can help there. 3. For political reasons, studies supporting 1 are far more likely to be conducted and published than 2. But that doesn't mean either that 2 is not true (which might seem the case because no studies support it) nor that 1 is not true (which might seem the case because of the political publication bias).