Cricket is right
LOW PAGE RANK is the main cause of Supplemental REsult..
The results you have on your site depends on the quantity and quality of the links you have..
Duplicate content is the side effect of the Supplementary Result..
Other causes of supplemental results are:
Lack of Trust
Manipulative linking practices can also lower PageRank flow into a domain, thus creating more supplemental pages.Manipulative links include excessive reciprocal linking, link injections, and paid links.
High Page Count
A large site with a high page count is also generally more vulnerable to the supplemental index than a small site because inbound PageRanks divided among several hundred thousand pages tend to be lower than that divided up among only a few dozen pages.
that is base on my readings!!!
