Would be great if you could find the citation, because this seems like the best explanation so far. There are only about 54 stars which at some point had a distance of less than 17 light years (that we know of): http://en.wikipedia.org/wiki/List_of_nearest_stars_and_brown... . Assuming that some stellar source of energy is required for life we can already remove 9 stars from that list because they only consist of brown dwarfs. Doing the math with the conservative estimates in the blog post, this puts the chance of detecting signs of life at a pretty low percentage. Assuming that 22% of these stars have at least one planet with earth like conditions and a 1% chance that some form of life develops on these planets, we arrive at the low chance of 46x0.22x0.01, ie. ~10% of finding any life in our vicinity.
