A survey by @RetentionSci found that percentage discount is the most effective customer incentive, free or discounted shipping is the second, amount discount the third, dynamic (personalized to customer shopping habits) the fourth, loyalty programs the fifth, and multiple purchase discount the sixth. Whether a consumer prefers free shipping to a percentage discount varies mostly by age. Respondents between the ages of 18 and 45 prefer a percentage discount to free shipping, while older digital shoppers prefer free shipping to a percentage discount. - Link