A subscriber is someone that is signed up for emails. A customer is someone that has ever made a purchase. The number of people that have made a purchase is growing, and the amount they buy per quarter has been steady at around $40 for the past year. The number of people that get the emails, but don't buy has been exploding so revenue per person on the email list has been steadily decreasing. You reached the conclusion that they will require more marketing spend based on a decreasing revenue per subscriber. I draw the opposite conclusion, that spending money to get more people to signup for the email list is probably counter productive becuase incremental customers are unlikely to purchase a groupon, and thus marketing expense should reduced. Same data, opposite conclusion.