Have you ever felt like your friends were more popular than you? Perhaps you’re a little insecure about how many sexual partners you’ve had, or the number of connections you have on LinkedIn. The friendship paradox, a term coined by sociologist Scott L. Feld in 1991, would suggest these fears are not without foundation. It’s down to sampling bias: You are more likely to be friends with someone who has more friends than you, simply because there is a greater chance that you will be friends with them. It’s a quirk that’s true of all social networks, whether they are in real life (most people’s sexual partners tend to be more promiscuous than they are) or virtual (your followers on Instagram are more likely to have more followers than you).¹ The phenomenon has even been used to...