How do you rate all-rounders?

We have devised an all-rounder index that gives a good indication of who the best all-rounders in the world are in Test and One Day cricket. To obtain the index, simply take the player's batting and bowling points, multiply them together and divide by 1000. So a player with 800 batting and 0 bowling gets an index of zero (because he can't bowl and therefore isn't an all-rounder!), 600 batting/200 bowling gets a rating of 120, and 400 batting/400 bowling points gets a rating of 160. An index of 300 plus is world class. There are far more all-rounders in T20s and ODIs than Tests, but the same names tend to appear high in both lists. Incidentally, this index does omit one important all-rounder skill, namely fielding. There is no satisfactory way of rating fielding skills statistically at present.