Drake's Equation

http://www.activemind.com/Mysterious/Topics/SETI/drake_equation.html

I am trying to make a good estimate of how many space civilizations there are, however I need your help /sci/ on giving me a good estimate for use variable.

There is no such thing as aliens, there is only Allah and his creations.

>>2
AHAHAHAHAHAHAHAHA!

I'd figure how long our planet has been around devided by how long we have been able to get into space? So (earth yrs)/(time been in space) or instead you could do years since the beginning of the universe minus how long it took multi-cellular organisms to come into existence since earth was made.

>>4
The one sample we have is obviously the statistical average.

>>5
No, but there has to be some sort of limit due to the limitations on cellular reproduction that would limit on how quickly multi cellular life forms... or whatever an alien would be made of. But a plant forming then right away there being intelligent life with technology seems a bit absurd.

Another thought is I wonder what % of planets have the materials necessary to support a technologically advanced civilization. What's to say most planets out there do not any appreciable or accessible amounts of metals?