In the spring in Ec 10, we will discuss how economists measure inflation using price indexes. Here is an offbeat example: The cost of "The Twelve Days of Christmas" is on the rise - again. Buying each item in the song just once - from a partridge in a pear tree to 12 drummers drumming - will cost you $18,920, or 3.1% more than last year, according to PNC Financial Services Group. The total cost of