Expectancy theory is a theory of motivation based on the belief that people’s efforts to achieve depend on their expectations of reward. Working within the framework of expectancy theory, Edwards (1954) and later Atkinson (1964) developed theories of motivation based on the following formula: Motivation (M) = Perceived probability of success (Ps) x Incentive value of success (Is).
The formula is called an expectancy model, or expectancy-valence model because it largely depends on the person’s expectations of reward. What this theory implies is that people’s motivation to achieve something depends on the product of their estimation of their chance of success (perceived probability of success, Ps) and the value they place on success (incentive value of success, Is).
Wigfield (1995) found that students’ beliefs that they were capable and their valuing of academic success were, taken together, more important than their actual ability in predicting their achievement.
Atkinson (1964) added an important aspect to expectancy theory in pointing out that under certain circumstances an overly high probability of success can be detrimental to motivation. Recent research has shown that a person’s motivation increases as task difficulty increases up to a point at which the person decides that success is very unlikely or that the goal isn’t worth the effort. This and other research findings indicate that moderate to difficult (but not impossible) tasks are better than easy ones for learning and motivation.