Original sentence: Estimated by Drake as 0.01.There is a lack of hard data to substantiate his choice of 1%, and could range anywhere from 0% to 100%.This is essentially unknowable with current technology, and statistically impossible to calculate since we have a sample-size of 1 (Earth)
Edited sentence: (See criticism).Estimated by Drake as 0.01 based on little or no evidence.Optimists note the generally increasing complexity of life and conclude that the eventual appearance of intelligence might be inevitable, meaning fi=1.Pessimists point out that of tens of millions of species on Earth, only one has become intelligent and infer a tiny value for fi.Skeptics point out that the large spread of values in this term and others make all estimates unreliable.This value remains particularly controversial