We aggregate CARIES level information to the higher TOOTH level and create a NEW LEVEL 1 that we call “TEETH”

(This aggregation is analogous to the ecological study design – see later)

We disregard the higher levels PLACE and INDIVIDUAL and disaggregate them to the NEW LEVEL 2 that we call “MOUTH”.

There are different levels and we can aggregate or disaggregate.

BUT

EVEN WHEN WE ARE INTERESTED IN A CONCRETE LEVEL (e.g., mouth) WE NEED TO CONSIDER ALL THE LEVELS…

AN ASSOCIATION AT THE MOUNTH LEVEL COULD IN FACT WE A PLACE EFFECT!!