Comparison of Two Peer Groups' Size

For a large$-$scale recommender system like Amazon.com, compare the size of two peer groups in UBCF and IBCF. Assuming that no external condition is imposed by the algorithm on the size of the groups, for the current user u and an item p:

The peer group of items is likely to be much larger than that of the users.

The peer group of users is likely to be much larger than that of the items.

The two peer groups are likely to be comparable in size.

Nothing can be said about the size of the two peer groups.