This landmark research from Northwestern University quantifies what every marketer suspects: reviews matter. Products with just 5 reviews are 270% more likely to be purchased than products with none. For higher-priced items, the effect is even stronger—conversion increases 380%.

Counter-intuitive finding: purchase likelihood peaks at 4.0-4.7 stars, then decreases as ratings approach 5.0. Perfect ratings appear 'too good to be true.' Verified buyer badges add 15% to purchase odds. After 5 reviews, marginal benefit diminishes rapidly.

The purchase likelihood for a product with five reviews is 270% greater than the purchase likelihood of a product with no reviews. For higher-priced items, reviews increase conversion by 380%.