Title says it all, my group has been using our ability score instead of ability mod and I've noticed that none of the creatures in the Monster Manual get such a high initiative bonus so early.
It's your dexterity modifier.
From the RC, p80 (emphasis mine):
Initiative Modifier: The character's initiative modifier includes the following numbers:
One-half the character's level
The character's Dexterity modifier
Racial or feat bonuses
Any other bonuses or penalties
There are very few things in 4e that use your actual ability score instead of the modifier. These include:
Consitution is added to your HP
Feats can list a specific ability score as a requirement
Strength determines how much you can carry