Chris Davis said:

The Drake equation is lacking some terms which have only come to light since it was formulated. I assume Dr. Boss' figures are based on an estimated of earth-sized planets in a Solar Habitable ('Goldilocks') Zone. Earth has other characteristics.

I think the requirement of being inside the "Goldilocks zone" has been more or less discarded in recent years. If our own Solar system is any indication, a world (like Europa) can be far outside the supposed Goldilocks zone and still produce life. Actually, these types of inhabited worlds are likely to be far more common than the type we live on, due to the sheer abundance of gas giants and the assumption that each of them is likely to have dozens of moons.

We have at least two other worlds right here in our own Solar System, besides the Earth, that could theoretically support life. If our current data is correct, we could transplant a deep-sea ecosystem from Earth to Europa and it would be right at home. And it looks very likely that there is at least microbial life on Mars. So Drake's equation might actually have turned out to be needlessly pessimistic. An average star system might be expected to have at least one or two life-bearing worlds throughout the galaxy.