the article "Xenopsychology" by Robert Freitas in Analog of April
1984 there is an interesting index called "Sentience quotient". It
is based on: The sentience of an intelligence is roughly directly related to
the amount of data it can process per unit time and inversely to the overall
mass needed to do that processing. This would be something like
baud/kilograms. And since that would rapidly turn into a real big number, base 10 logs are used. The "least sentient"
would be one bit over the lifetime of the universe massing the entire known
universe, or about -70. The "most sentient" is claimed to be +50.
Homo sapiens are around +13, a Cray I is +9, a venus flytrap is a peak of +1
with plants generally -2. [AS]