This was an interesting blue comment I found, in a thread about how one realm claimed to be 7.6:1 horde:alliance:

The faction balance is almost a perfect 2:1, horde heavy, which is fairly normal for PvP realms. PvE tends to be alliance heavy at about 2:1, so it's flipped but definitely within an acceptable difference and comparison to other realms.

I would not have guessed those ratios were normal. :P