### Approval Measures My Way

Amazon has a rating for its books where it combines all the customer reviews to obtain an average rating on a scale from 1 to 5 stars. This is all well and good. A high average or a low average would tell me something useful about the book. Middling reviews, however, fall into two distinct classes. The first class is that of

**good, but uninspiring**books. The second class is that of

**controversial**books, regardless of technical merit.

The average rating in Amazon is informative. They also give the number of reviews, which is probably a better indicator of interest value. Amazon will shade part of a star to give a little more precision. I've seen some approval ratings that give a decimal point, e.g. 4.3 stars out of 5. I kind of like that better. What I'd really like to see (sorry to force this on you) are the **standard deviations**. I'd kind of like to see standard deviations on every composite measure I see (maybe even a box and whiskers chart <----[===]----->).

You may remain unconvinced, but consider: A four-star book with a standard deviation of 0.8 stars is relatively non-threatening. A four-star book with a standard deviation of 1.5 stars may just be too hot to handle. And a three-star book with a standard deviation of 2.0 stars will blow off the shelves, because itâ€™s by or about the Clintons.

6/30/2005 9:07 AM