Meaning of redo wastage

In the Bstat Estat report, there is a line called redo wastage. Mine has a value of
49.66% per transaction. What gives? What does it mean,and how do I fix it?
I have 3 rollback segments sized at initial 16M next 16M minextents 20 - for a pretty
good size, not too much growing and shrinking going on. This if for a datamart app
that is undergoing some test loads at the moment...

• Dc.