What is the Unit of Measurement for a Selection Index?

Matthew Spangler (University of Nebraska - Lincoln): Those are really represented in dollars per head of either added income or, hopefully, increased profit for a sire's progeny. So, if we think about two bulls, both having the same economic index value, let's say that one bull is 100 and the other bull has an index value of 50, then we can say that the bull with the index value of 100, on average, his calves would average $50 more per head in added income if we market our animals according to the assumptions of the index.