That's a very tough one, because the number of complaints filed doesn't tell the story at all. If you have an organization that has 40 complaints filed, it could mean that people feel safe coming forward and that the organization will take action. If you have an organization that has zero complaints filed, it could mean that people are scared or that people don't trust management or whatever.
I think the survey is one good indicator of whether harassment is happening. People can say whether they perceive that they have been harassed. That doesn't mean they have been. That's their perception.
That would be one of the best approaches to measure that.