Most of the sensory evaluation carried out by a trained panel involves measurement in two main areas, difference testing and descriptive analysis. Sensory difference tests are procedures used to determine whether judges can distinguish between two similar stimuli. In terms of food, the two stimuli are two very similar food samples. These evaluations are used to determine whether slight changes occur due to either product reformulation or the change in technological processing. Difference tests are particularly well adapted to the assessment of vegetable oils during their processing, being used to control refining efficiency.