A feedback loop occurs when a model influences the world that later supplies its data. Recommendations can change which items become popular, so future training data reflects earlier model choices. section 6.3 section 14.4
Popularity reinforcing itself
A marketplace recommends items using current popularity. An item may then gain more attention and become even more popular, reinforcing its place in later recommendations. Recording when samples were generated and which system versions were live can help investigate this pattern, though metadata alone is not enough to avoid it. section 6.3 section 14.4
Feedback loops also complicate online testing: historical data shows what was recommended, but not exactly what would have happened if a user had seen a different item. Interpret results with that uncertainty in mind. section 12.0





























