Most Powerful Women list: How we do it

Who’s more powerful–Oprah Winfrey or Yahoo CEO Carol Bartz? Disney media boss Anne Sweeney or MTV Networks chief Judy McGrath? Who from Google made the 2009 Fortune Most Powerful Women list?

The new rankings are out. PepsiCo CEO Indra Nooyi is No. 1 for the fourth year in a row.

And yes, there is a science to deciding these rankings. Here I talk with CNNMoney anchor Poppy Harlow about how we do it: