Theory revision[edit]
The theory has even been revised and extended by Ajzen himself into the theory of planned behavior. "This extension involves the addition of one major predictor, perceived behavioral control, to the model. This addition was made to account for times when people have the intention of carrying out a behavior, but the actual behavior is thwarted because they lack confidence or control over behavior" (Miller, 2005, p. 127).
Ajzen's revised conceptual model, accounting for actual behavioral control, can be expressed as follows: