I ran across two links posted in the past, and I thought it might be helpful to repeat them here.  Bob posted a link to an SEC document directly from TIAA-CREF, March, 2007, which included both standard deviations and correlations for the REA:

8-K March, 2007 

and TallyMan downloaded some figures from the TIAA-CREF public web site, and used them to compute his correlations based on quarterly data:

Conversation 1479  Then go down to the 3rd post, Post #2364959

These suggest that the REA isn't very "like" either stocks or bonds, but has been a good diversifier for it's relatively short life span (compared to the record-keeping periods for stocks and bonds.)

Tim