Amri Wandel
The data recently accumulated by the Kepler mission have demonstrated that small planets are quite common and that a significant fraction of all stars may have an Earth-like planet within their Habitable Zone.
These results are combined with a Drake-equation formalism to derive the space density of biotic planets as a function of the relatively modest uncertainty in the astronomical data and of the (yet unknown) probability for the evolution of biotic life…
…Read more at http://arxiv.org/ftp/arxiv/papers/1412/1412.1302.pdf

Read also: How Data From The Kepler Space Telescope Is Changing The Drake Equation