Human Factors is the scientific study of how our environment and sensory world translate into our decisions and actions. Human Factors is often applied to questions of liability. Did a person detect and respond to a critical stimulus in a typical way? Or was their response or action atypical and suggestive of inattention? Can a person be expected to anticipate a particular hazardous event? These questions are often raised after traffic collisions, pedestrian trips, and injuries from products. Analysis of lighting, conspicuity, driver and pedestrian behavior, product warnings, and injury statistics can help quantify perception and action, rather than relying on qualitative descriptions based on subjective experience.