If you’ve been wondering whether LinkedIn’s stock — selling as I write this for about $72 a share, down from a high of $122.70 during its first day of trading May 19 — is (or at least was) in a bubble, Robert Jarrow, Younes Kchia, and Philip Protter have an answer for you. The trio (respectively, a finance professor at Cornell, an applied-math Ph.D student at the Ecole Polytechnique, and a statistics professor at Columbia) developed a statistical technique for detecting bubbles that they tested on data from the dot-com heyday.