Mega Extra Terrestrial Assay

It seems to me that the Drake equation has so many terms that are known with such little accuracy that one could get most any kind of answer one wants. Until we explore the planets of a couple hundred stellar systems and log how many evidences of life we find we will have no practical ability to do any meaningful calculation.

Being from the chemistry and life sciences I have often wondered if the search can be narrowed to planets at a solar distance that keeps water or hydrogen sulfide in the liquid state. I am of the idea that life will always be carbon based due to the tetrahedron and 4 bonding sites. Organic molecules dissolved in water allow for both hydrophillic and hydrophobic interaction and this expands the capabilities of molecules to carry out life processes. So some equation that would allow a search at specific orbits derived from Bode's Law and integrated with the stars magnitude and size may provide a filter for searching other systems for their "Earths" - MV