<P> As many skeptics have pointed out, the Drake equation can give a very wide range of values, depending on the assumptions, and the values used in portions of the Drake equation are not well - established . In particular, the result can be N ≪ 1, meaning we are likely alone in the galaxy, or N ≫ 1, implying there are many civilizations we might contact . One of the few points of wide agreement is that the presence of humanity implies a probability of intelligence arising of greater than zero . </P> <P> As an example of a low estimate, combining NASA's star formation rates, the rare Earth hypothesis value of f n f = 10, Mayr's view on intelligence arising, Drake's view of communication, and Shermer's estimate of lifetime: </P> <Dl> <Dd> R = 1.5--3 yr, f n f = 10, f = 10, f = 0.2, and L = 304 years </Dd> </Dl> <Dd> R = 1.5--3 yr, f n f = 10, f = 10, f = 0.2, and L = 304 years </Dd>

Estimate the fraction of stars that have planet