Page "Collaborative filtering" Paragraph 53

Collaborative filters are expected to increase diversity because they help us discover new products among myriad choices.

Some algorithms, however, may unintentionally do the opposite.

Because collaborative filters recommend products based on sales or ratings, they cannot usually recommend products with limited historical data.

This creates a rich-get-richer effect for popular products, leading to less diversity.

A Wharton study details this phenomenon and several ideas which may promote diversity in collaborative filtering recommendations.