Amazon Prime is a vital part of the company's e-commerce business: customers who belong to the $99-per-year loyalty program spend more than twice as much as people who don't, according to several $4.
It's also growing like wildfire. New data from $4 shows that half of all households in the United States are Prime members, up from about 35% two years ago. The penetration is highest, and growing fastest, among upper-income households with more than $112,000 a year in annual income - more than 70% of households in that demographic have a subscription, up from less than half two years ago.
Piper Jaffray
Disclosure: Jeff Bezos is an investor in Business Insider through hispersonal investment company Bezos Expeditions.