What typically happens is that plants are extracted,the extract is dried and made up to a known concentration and bioassay is carried out on this solution. If the solution has a high or low activity, it is automatically inferred that the original plant also has a high or low activity. To compare the plants however, the quantity extracted from the plant should obviously be brought into the equation. If an extractant extracts say 20% of the dry plant material of plant A (i.e. 200 mg extracted from 1 g) and the extract has an antioxidant activity of 0.6 trolox equivalent it has a much higher total anti oxidant activity than plant B extracting 2% of the dry mass (i.e. 20 mg extracted from 1 g) with a trolox activity of 1.2 trolox equivalent. Looking at a table with the antioxidant activities of the extracts one would have concluded that plant A is twice as active as plant B and would be a good source for bioprospecting.