John Stacey Adams, workplace and behavioural psychologist, put forward his Equity Theory on job motivation in 1963. and other pioneers of workplace psychology, in that the theory acknowledges that subtle and variable factors affect each individual's assessment and perception of their relationship with their work, and thereby their employer. Equity (or inequity) is a psychological state residing within an individual. Equity is a social comparison process, resulting when individuals compare their pay to the pay of others.

Equity is a subjective evaluation, not an objective one. Individuals determine equity by comparing their contributions (job inputs) and their rewards (job outcomes) to those of the their comparisons. A unions interest lies in achieving equity for the greatest number of its members, regardless of their ability to leave the organization. Five major approaches that have led to our understanding of motivation are Maslow's need-hierarchy theory, Herzberg's two- factor theory, Vroom's expectancy theory, Adams' equity theory, and Skinner's reinforcement theory.

Vroom's theory is based on the belief that employee effort will lead to performance and performance will lead to rewards (Vroom, 1964). Adams' theory states that employees strive for equity between themselves and other workers. Skinner's theory simply states those employees' behaviors that lead to positive outcomes will be repeated and behaviors that lead to negative outcomes will not be repeated (Skinner, 1953). A comparison of these results to Maslow's need-hierarchy theory provides some interesting insight into employee motivation.