According to the “light-hearted” Christmas edition of the British Medical Journal, Playboy’s Playmates have gotten more androgynous over the years:
http://story.news.yahoo.com/news?tmpl=story&u=/ap/20021220/ap_on_fe_st/centerfold_curves_1
I don’t buy it. The “top” measurement on any of the Playmates I’ve seen exceeds the "Middle’ by a consioderable amount, and usually even the “Bottom” by a bit.
I may have to conduct my own study.
Hmmmm. I don’t know any libraries that stock back issues of Playboy. I wonder where they got their data?
Yes more research is needed, I’ll get back to you on the OP. 
I’ve seen them all. And a lot of those early centerfolds had extremely accentuated hips like the one on the left here and in the photo.
I don’t think that’s too natural nor common nowadays. Of course I haven’t seen a flesh and blood naked woman in 5 years.
P.S. I searched around that link (before posting) and found no nudity. It appears to be only related to the Playboy nightclub and the bunny waitresses.
I don’t think I’ve ever seen a woman with a waist-to-hip ratio like that without the aid of a corset. A little whale bone can go a long, long way. It’s funny that they should do a study like this, because my boyfriend (a Playboy collector) said last year how they should bring back more Bettie Page/ Marilyn Monroe types because the girls are slowly beginning a gradual descent into runway thinness.
A friend just sent this link to me.
"Click this link and you can look at every playboy centerfold since 1954 until last month !!! 50 years of photos with 12 photos per year "
http://rosbif.free.fr/playboy/img/
CAUTION! I’m at work, haven’t opened it, and I’m not going to open it here.
It may be legit, it may be a hoax, it may be porn. Click at your own risk. 
It’s a 404 error. I know the link of which you speak, and you can find it on www.fhm.com Or at least you could a few weeks ago. Indeed it is every playmate of the month, every last one.