2008 study. Do a Google search for:  Kim Bergholdt, Rasmus N Fabricius, Tom Bendix
then click on the link from www.medscape.com/

2003 study. Do a Google search for: mattresses Francisco Kovacs
then click on the link from www.medscape.com/

1981 study. Do a Google search for:  S R Garfin, S A Pye
then click on the link from www.medscape.com/

I hope even more extensive research is done in the future and becomes available to the general public. This is just what I could find tonight.

Matt

http://www.rebuildyourback.com/backpain/1963964.php 
This sums up the studies pretty well.  Clear as mud!  Generally, new beats old, medium firm beats extra firm, and almost everything is better than a really hard futon.
; }
Kait