7
Two modifications
¢Sparse
data
lDefault
Voting
•Users would agree on
some items that they didn’t get
a chance to rank
•Assume all unobserved items have neutral or negative ranking.
•Smoothes
correlation values in sparse data
¢Balancing
Votes:
lInverse
User Frequency
•Universally
liked items not important to correlation
•Weight (j) =
ln (# users/# users voting for item j)