  We develop a simple statistical method to find affinity relations in a large
opinion network which is represented by a very sparse matrix. These relations
allow us to predict missing matrix elements. We test our method on the
Eachmovie data of thousands of movies and viewers. We found that significant
prediction precision can be achieved and it is rather stable. There is an
intrinsic limit to further improve the prediction precision by collecting more
data, implying perfect prediction can never obtain via statistical means.

Physics and Society