<P> The Drake equation is a probabilistic argument used to estimate the number of active, communicative extraterrestrial civilizations in the Milky Way galaxy . The number of such civilizations N, is assumed to be equal to the mathematical product of </P> <Ol> <Li> R, the average rate of star formations, in our galaxy, </Li> <Li> f, the fraction of formed stars that have planets, </Li> <Li> n for stars that have planets, the average number of planets that can potentially support life, </Li> <Li> f, the fraction of those planets that actually develop life, </Li> <Li> f, the fraction of planets bearing life on which intelligent, civilized life, has developed, </Li> <Li> f, the fraction of these civilizations that have developed communications, i.e., technologies that release detectable signs into space, and </Li> <Li> L, the length of time over which such civilizations release detectable signals, </Li> </Ol>

What is the purpose of the drake equation