[InitialLastName]

> but I guess it would be easy to find volunteers.

I don't know, in my experience people are sure picky about procreating with random strangers (and the ethical concerns regarding the output of the study are... significant).

From people I've known undergoing fertility treatments (and from my own limited research), the issue is frequently traceable to a specific cause in one or both partners (although it appears to be unexplained in about 20% of couples who seek treatment, which would be a small subset of the general population).