Only applies to items that exist in both sets of data

**Change in Price**

    ( P₂ - P₁ ) Q₂

**Change in Quantity**

    ( Q₂ - Q₁ ) P₁

_To further break out change in quantity_


Change in Quantity - _Volume Related_

    Q₂ ( Q₁ / Σ ( Q₁ ) ) - Q₁

Change in Quantity - _Mix Related_

    Q₂ - Q₂ ( Q₁ / Σ ( Q₁ ) )