Re: here's whats weird about this (more) (archive)

I took a look at the X-5 review in this new issue. What I found really strange was the X-5 received all red circles or clear circles in all areas but no black circles. This means it did pretty well since a full red circle is the best rating possible.

Black circles are the worst rating. Then when they gave a future reliability rating. They gave a full black circle? Now how do all reds and clears average into a black?

I have no connection with CR, so this is just a guess, but I'm pretty sure that what is going on is that the black circle is "compared with other new vehicles", while the individual circles by area are on absolute scales which are explained just before the individual vehicle ratings start. The full red circle means less than 2% of respondents of their survey reported a problem in that area. The partial red means 2-5%, etc. (Or some such numbers.) These absolute circles are not corrected for age in any way, so you would expect more black circles for older model years, and this is on the whole what you see. Thus, almost all new model year cars have few black circles, but since the overall circle rating is compared with other new models (compared with the average) some of them have to have black circles.

I don't think this is explained terribly well. But the nice thing is that by looking at the individual circles you actually have absolute information (x% chance of problem in that area in the next Y months).

-Karl, kpfleger@cs.stanford.edu

http://www-cs-students.Stanford.EDU/~kpfleger/auto/safest_car.html

Follow Ups:

Great website Karl, lots of interesting info! Bimmerguy 10:44 11/26/2001 (0)

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