Used in construction of stock indices. Suppose there 10 stocks in an index, each worth $10 and the index is at 100. Now suppose that one of the stocks must be replaced with another stock that is worth $20. If no adjustment is made to the divisor, the total value of the index would be110 after the swapping. yet there should be no increase in value because nothing has happened other than switching the two constituents. The solution is to change the divisor; in this case from 1.00 to 1.10. Note that the value of the index, 110/1.1, is now exactly 100 - which is where it was prior to the swap.
Copyright © 2011 Campbell R. Harvey, Professor of Finance, Fuqua School of Business at Duke University