From the paper:

A Bioavailability Score, ABS, is formulated as the probability that a compound will have >10% bio-availability in rat or measurable Caco-2 permeability. ABS is 0.11 for anions for which PSA is >150 Å2, 0.56 if PSA is between 75 and 150 Å2, and 0.85 if PSA is <75 Å2. For the remaining compounds ABS is 0.55 if it passes the rule-of-five and 0.17 if it fails.