Difficulty is considered a key predictor of behavior in
psychology and is included in most recognized models of behavior change, such as the
theory of planned behavior. Most of these models rely on people's perceptions and estimates of behavioral difficulty. That is, difficulty is considered to be subjective and person-dependent. Obviously, perceived difficulty varies by individual. A more objective measure of difficulty is desirable, e.g., for
environmental or
energy policy, because people may misperceive the difficulty of behaviors, possibly because affected by mood or current circumstances. == The Campbell Paradigm ==