We can start by taking the average rate of star formation (R*) in our Galaxy, the Milky Way. A strange factor to consider perhaps, but understanding how many stars form each year allows us to ultimately consider how many civilizations are born each year. Current theory suggests this number, in the Milky Way, is about 10 new stars per year.
The second item fр defines the fraction of those stars which have planets and, according to current scientific values, is something like 50 percent.
Of the remaining values, we can actually look closer to home and learn from our very own solar system. Taking ne and fΙ, which explain the number of planets that can support life and the fraction of those planets where life actually evolves, and applying to the Solar System, will suggest a couple of possible options.
Obviously, Earth can support life (as we know it) and perhaps in the past so has Mars, this gives us an answer of 2 for the first point but we should also perhaps consider Europa and Titan as they, too, may harbor conditions where life, however primitive or weird, may be able to evolve, giving us an answer of 4 instead. The fraction where life evolves is at least 1 but it's thought that if the conditions are right, then life will evolve to some degree, at some time, leaving f We can then apply some decent and pretty reliable numbers to the final factors in Drake's equation. fⁱ is the fraction of those life bearing planets where intelligent life evolves. From our own Solar System we know of only one place where intelligent life has evolved (although sometimes I do wonder) leaving us with 25 percent.