The most popular extension and refinement of Maslow's theory of needs is the one proposed by alderfer (1972). While Maslow's model was not developed specifically for work organizations, alderfer's theory attempted to establish a conceptualization of human needs that are relevant to organizational settings. In extending Maslow's theory, alderfer argued that the need categories could be grouped into three general classes:
1) Existence: these are needs that involve interpersonal relationships in the work place. Relatedness needs are similar to Maslow's belongingness needs and certain of his safety and esteem/ego needs.
2) Relatedness: these are needs that involve interpersonal relationships in the work place. Relatedness needs are similar to Maslow's belongingness needs and certain of his safety and esteem/ego needs.
3) Growth: these are needs associated with the development of the human potential. Included in this category are needs corresponding to Maslow's self-actualization needs.
Alderfer's model agree with Maslow's in positing that individuals tend to move from existence, through relatedness, to growth needs as needs in each category are satisfied.
However, ERG theory differs from the needs hierarchy model in two important respects. First, alderfer contends that, in addition to the satisfaction-progression process described by Maslow, a frustration-regression sequence also exists. For example, the ERG model predicts that if an individual is continually frustrated in his or her attempts to satisfy growth needs, then relatedness needs will be reactivated and become the primary drivers of behavior. Second, and especially important, in contrast to the needs hierarchy theory, the ERG model does not hold that one level of needs must be satisfied before needs in the next level can emerge to motivate behavior. Instead, the ERG model proposed that more than one need may be operative in a given individual at any point in time the ERG model appears to be less rigid than the needs hierarchy theory, allowing for more flexibility in describing human behavior.