SETI takes its cue from a 1961 formula called the Drake Equation, which was created to hypothesize the number of civilizations in our galaxy with which we might be able to communicate. That number ranges widely because the variables in the equation necessitate educated guesses and estimations. It would stand to reason that the formula would have been refined over the years, but the New York Times is reporting that that is not the case. It has held up surprisingly well (for such a nebulous equation, "held up" is a relative phrase). Data collected since the 1960s, which can be used to support the original estimates, has proven those estimates to have been accurate. The rest will likely always leave us to wonder.