Are you calculating Monero to USD? If not then it'll be a flawed comparison.
Why? There is no such thing as a Monero/USD trading pair. It doesn't exist in nature.
You can get the usd value by converting the bitcoin value to usd for that exact time.
OK I can do this for you too, but I can tell you now it won't matter, Monero is still more volatile than bitcoin. I'll have to do it tomorrow though, unless you want to do it first. Be my guest.