Editing Drake equation (section)

===Original estimates===
There is considerable disagreement on the values of these parameters, but the 'educated guesses' used by Drake and his colleagues in 1961 were:<ref name="Drake 1961" /><ref>
{{cite book
 | last1 = Drake | first1 = F.
 | last2 = Sobel |first2 = D.
 | year = 1992
 | title = Is Anyone Out There? The Scientific Search for Extraterrestrial Intelligence
 | pages = 55–62
 | publisher = [[Delta (publisher)|Delta]]
 | isbn = 0-385-31122-2
}}</ref><ref>
{{cite journal
 |last1=Glade |first1=N.
 |last2=Ballet |first2=P.
 |last3=Bastien |first3=O.
 |year=2012
 |title=A stochastic process approach of the drake equation parameters
 |journal=[[International Journal of Astrobiology]]
 |volume=11 |issue=2 |pages=103–108
 |arxiv=1112.1506
 |bibcode=2012IJAsB..11..103G
 |doi=10.1017/S1473550411000413
|s2cid=119250730
 }} Note: This reference has a table of 1961 values, claimed to be taken from Drake & Sobel, but these differ from the book.</ref> 
* {{math|''R''<sub>∗</sub>}} = 1 yr<sup>−1</sup> (1 star formed per year, on the average over the life of the galaxy; this was regarded as conservative)
* {{math|''f''<sub>p</sub>}} = 0.2 to 0.5 (one fifth to one half of all stars formed will have planets)
* {{math|''n''<sub>e</sub>}} = 1 to 5 (stars with planets will have between 1 and 5 planets capable of developing life)
* {{math|''f''<sub>l</sub>}} = 1 (100% of these planets will develop life)
* {{math|''f''<sub>i</sub>}} = 1 (100% of which will develop intelligent life)
* {{math|''f''<sub>c</sub>}} = 0.1 to 0.2 (10–20% of which will be able to communicate)
* {{math|''L''}} = somewhere between 1000 and 100,000,000 years

Inserting the above minimum numbers into the equation gives a minimum N of 20 (see: [[#Range of results|Range of results]]). Inserting the maximum numbers gives a maximum of 50,000,000. Drake states that given the uncertainties, the original meeting concluded that {{math|''N'' ≈ ''L''}}, and there were probably between 1000 and 100,000,000 planets with civilizations in the [[Milky Way]] Galaxy.