TITLE: Complete problems for randomized complexity classes
QUESTION [7 upvotes]: It is believed that $BPP$ has no complete problems. Even for $BPP^O$ for a suitable oracle $O$ it is believed not to have complete problems, unless P=BPP. I wonder if the class MA (the randomized version of NP) has complete problems. For example, IP has complete problems (given that it is equal to PSPACE). There is a similar post asking about complexity classes with no complete problems. Here, I'm interested specifically on complete problems for MA. If the answer is positive, can you give some examples? I've tried google and the complexity zoo, but with no success.

REPLY [5 votes]: My own favorite complete problems are promise problems for the promise problem
version of SZK (Statistical Zero-Knowledge). These complete problems have played
a major role in the study of SZK, and the relations among them are fascinating per se.
See "On the complexity of computational problems regarding distributions (a survey)" 
at http://eccc.hpi-web.de/report/2011/004.
Oded