I believe the statistics, because I have some personal experience in these matters. And when it's just me and a girlfriend, talking over a glass of wine, and that issue comes up, she'll also speak softly about her experience, and how she too, didn't report it. And that happens time and time again. It is, unfortunately, an issue that binds many women together, a shared experience, perpetuated against us, by the men in our lives.
I'd go as far as to say, from my experience, that the statistics are greater than 1 in 5.