I've been collaborating with a bunch of free software projects during decades. Despite my origins and my bad English never ever have I felt excluded, on the con

I've been collaborating with a bunch of free software projects during decades. Despite my origins and my bad English never ever have I felt excluded, on the contrary, people were more than happy to help. I've never heard of someone excluded from a free software project due their origins. I would have expected from a highly technical community to implement measures based on facts and studies, not based on a hunch. Where are the studies showing the amount of discrimination before and after implementing a code of conduct in different projects?