Section 4.5.1 says:
"The third line shows how it is based on item-item similarities, not
user-user similarities as before. The algorithms are similar, but not
entirely symmetric. They do have notably different properties. For
instance, the running time of an item-based recommender scales up as the
number of items increases, whereas a user-based recommender’s running
time goes up as the number of users increases.
This suggests one reason that you might choose an item-based
recommender: if the number of users is relatively low compared to the
number of items, the performance advantage could be significant."
Shouldn't the second paragraph be?
"This suggests one reason that you might choose an item-based
recommender: if the number of users is relatively *high* compared to the
number of items, the performance advantage could be significant."
