1. A method of characterizing the effect of a stimulus on hepatocytes, the method comprising: (a) exposing a first sample of hepatocytes to a stimulus under a first set of conditions; (b) exposing a second sample of hepatocytes to the stimulus under a second set of conditions; (c) imaging the first and second samples; (d) extracting first features from one or more images of the first sample and second features from one or more images of the second sample; and (e) analyzing features extracted from images of both the first sample and the second sample to assess the effect of the stimulus on hepatocytes.