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 it’s by or about the Clintons.

6/30/2005 9:07 AM