Do Friends Influence Purchases in a Social Network?

• Executive Summary:
  In spite of the cultural and social revolution in the rise of social networking sites such as Facebook and MySpace (and in South Korea, Cyworld), the business viability of these sites remains in question. While many sites are attempting to follow Google and generate revenues from advertising, will advertising be effective? If friends influence the purchases of a user in a social network, it could potentially be a significant source of revenue for the sites and their corporate sponsors. Using a unique data set from Cyworld, this study empirically assesses if friends indeed influence purchases. The answer: It depends. Findings are relevant for social networking sites and large advertisers. Key concepts include:
• There is a significant and positive impact of friends' purchases on the purchase probability of a user.
• However, there are significant differences across users. Specifically, this social effect is zero for 48 percent of the users, negative for 12 percent of the users, and positive for 40 percent of the users.
• "Moderately connected" users exhibit "keeping up with the Joneses" behavior. On average, this social influence translates into a 5 percent increase in revenues.
• Highly connected users tend to reduce their purchases of items when they see their friends buying them. This negative social effect reduces the revenue for this group by more than 14 percent. This finding is consistent with the typical fashion cycle wherein opinion leaders or the elite in the fashion industry tend to abandon one type of fashion and adopt the next in order to differentiate themselves from the masses.
  Abstract
  Social networks, such as Facebook and Myspace have witnessed a rapid growth in their membership. Some of these businesses have tried an advertising-based model with very limited success. However, these businesses have not fully explored the power of their members to influence each other's behavior. This potential viral or social effect can have significant impact on the success of these companies as well as provide a unique new marketing opportunity for traditional companies.
  However, this potential is predicated on the assumption that friends influence user's behavior. In this study we empirically examine this issue. Specifically we address three questions - do friends influence purchases of users in an online social network; which users are more influenced by this social pressure; and can we quantify this social influence in terms of increase in sales and revenue.
  To address these questions we use data from Cyworld, an online social networking site in Korea. Cyworld users create mini-homepages to interact with their friends. These mini-homepages, which become a way of self-expression for members, are decorated with items (e.g., wallpaper, music), many of which are sold by Cyworld. Using 10 weeks of purchase and non-purchase data from 208 users, we build an individual level model of choice (buy-no buy) and quantity (how much money to spend). We estimate this model using Bayesian approach and MCMC method.
  Our results show that there are three distinct groups of users with very different behavior. The low-status group (48% of users) are not well connected, show limited interaction with other members and are unaffected by social pressure. The middle-status group (40% users) is moderately connected, show reasonable non-purchase activity on the site and have a strong and positive effect due to friends' purchases. In other words, this group exhibits "keeping up with the Joneses" behavior. On average, their revenue increases by 5% due to this social influence. The high-status group (12% users) is well connected and very active on the site, and shows a significant negative effect due to friends' purchases. In other words, this group differentiates itself from others by lowering their purchase and strongly pursuing non-purchase related activities. This social influence leads to almost 14% drop in the revenue of this group. We discuss the theoretical and managerial implications of our results.
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