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Estimating Audience Size on Facebook

How many people do you think see the content you share on Facebook? Most likely you’re wrong.


Evidence from our new study with Stanford University suggests that our intuitions for the number of friends we reach on social media can be wildly inaccurate. We showed participants a recent post they made and asked them to estimate how many friends saw it. While the median participant guessed that 20 friends saw their post, it actually reached four times as many friends. At the same time, people also said that they wanted more of their friends to see their posts. So Facebook users tend to want larger audiences — but they probably already have them!


An audience survey

Audience considerations are core to sharing in social media. Our expectations about who’s listening affect how we present ourselves online. But there are a number of factors that could affect who see your post: the time of day when you write it, the people who respond to it, and a variety of systems that rank and recommend it to other users.


To better understand how well users’ intuition about audience reflects reality, we surveyed 1,131 users, pointing them to a recent post and asking how many friends they thought saw it, and then compared their answers to actual story views; all data was analyzed in aggregate to protect user privacy. We also asked users how satisfied they were with their audience size and what clues they use to estimate their audience.


By and large, people underestimated the size of their audience. When we asked users how many friends saw a particular post, the median user guessed 20 friends, while the actual median was 78. The figure below shows users’ perceived and actual audience sizes for a particular post. Each point represents a person, and the location of that point on the horizontal axis represents their actual audience size (as a percentage of their friends), and the vertical axis represents their estimated audience size. When points fall below the diagonal line, that individual underestimates the size of their audience.



Theories of audience size

Next, we wanted to understand what clues people use to estimate the size of their audience. People typically use the number of likes and comments they received. For example, one respondent explained, “I figured about half of the people who see it like it or comment on it.” The next most common strategy was to guess some fraction of their friend count, such as 20% of their friends. Others made a rough guess as to how many people might log into Facebook around the time that they posted the content.


Predictability of audience size

What makes people’s audience sizes so difficult to guess? We used data on these very same features that users relied on — friend count, likes, and comments — to see how predictive they were of audience size, for a slightly larger sample of users (approximately 220,000).


The figure below shows the size of users' audience as a function of the users' friend count. The center line represents the median number (left) or fraction (right) of friends, while the deep red band indicates the upper and lower quartile -- that is, the range of 50% of the users with the given friend count. The lighter bound indicates the 90% region. The figure highlights that even users with the same number of friends can have a great deal of variation in their audience sizes.



Next, we examined whether feedback such as likes and comments might be better predictors of audience size. The picture was similar to the one with friend count: audience sizes are highly variable, and difficult to predict, even if you think you might have a good sense of which friends might be listening.  We found that feedback was not well correlated with how many friends see a post. Below, we can see that for example, if a user receives 1 comment, 90% of the time, between 10-40% of their friends might have seen it, whereas if they received 4 comments, between 18-44% saw it. This makes it difficult to estimate one's audience size from feedback alone.



A final thought

So as you use Facebook over the course of a month or year, how many people see your posts? Your audience size is actually more stable over longer time periods. We found that the median user reaches 60% of their friends over the course of a month.


About the research

This research was conducted by Michael Bernstein, Eytan Bakshy, Moira Burke, and Brian Karrer, and won an honorable mention in the best paper competition at the Conference on Human Factors in Computing Systems (CHI) 2013. You can find out more about the details of our study here:


Quantifying the Invisible Audience in Social Networks. M. Bernstein, E. Bakshy, M. Burke, & B. Karrer. CHI 2013, April 27–May 2, 2013, Paris, France.