Drake's equation provides a way to quanitatively estimate the number of civilizations present in our Galaxy that are are technically able to communicate.
N = R*fp*ne*fl*fi*fc*L
** We might wish to restrict this to solar type stars or otherwise consider only "suitable" stars.
*** This implies a willingness to make the effort to use technology to communicate. We've been broadcasting I Love Lucy for decades, but the signal will quickly fade thanks to the inverse square law. Even if another species can detect this broadcast from many light-years away, would this constitute a recognizable attempt at intelligent communication?