The Wall Street Journal reports:

Facebook is struggling to detect and deal with users’ creating multiple accounts on its flagship platform, according to internal documents that raise new questions about how the social-media giant measures its audience.

An internal Facebook presentation this spring called the phenomenon of single users with multiple accounts “very prevalent” among new accounts. The finding came after an examination of roughly 5,000 recent sign-ups on the service indicated that at least 32% and as many as 56% were opened by existing users. The company’s system for detecting such accounts also tends to undercount them, according to the presentation, which was viewed by The Wall Street Journal.

A separate memo from May said that the number of U.S. Facebook users who are in their 20s and active at least once a month often exceeds the total population of Americans their age. “This brings out an elephant in the room: SUMA,” the memo’s author wrote, using an internal abbreviation for “Single User Multiple Accounts.” The author added that the issue could render Facebook’s ratio of users active each day “less trustable.”

At issue is the reliability of information that helps inform some big advertisers’ spending decisions. While Facebook says it doesn’t bill advertisers based on its estimates of an ad’s target audience, some advertisers look at those estimates when planning where to allocate their budgets—especially big brands that have turned to Facebook to reach large audiences as broadcast and cable television viewership have declined. [Continue reading…]