The present application discloses a method of adjusting a parameter, the parameter being used to derive a physiological characteristic of an individual from an image of the user, the method comprising the steps of: obtaining the parameter for the individual； obtaining a corresponding parameter for a plurality of other individuals within a cohort of the individual； comparing the parameter for the individual with a statistically significant parameter for the plurality of other individuals； and adjusting the parameter for the individual in accordance with the difference between the parameter for the individual and the statistically significant parameter for the plurality of other individuals.
