The International Data Corporation has based this prediction on a variety of different factors as reported by Gamespot. One of the main factors they feel the PS4 will win this season is because of the price gap. The PS4 sells for $399 while the Xbox One costs $499.
They also feel that Sony, Microsoft and Nintendo will be the main console providers until at least 2017. They feel outside competitors like Valve/Steam, Ouya or anyone else wanting to enter the console market won’t make an impact sooner than that.