Need for power
Need for power (nPow) is a term that was popularized by renowned psychologist David McClelland in 1961. McClelland's thinking was influenced by the pioneering work of Henry Murray who first identified underlying psychological human needs and motivational processes (1938). It was Murray who set out a taxonomy of needs, including achievement, power and affiliation - and placed these in the context of an integrated motivational model. McClelland was inspired by Murray’s research, and he continued to further develop Murray’s theory by focusing on this theory in regard to the human population. In McClelland's book The Achieving Society N-Pow helps explain an individual's imperative to be in charge. According to his work there are two kinds of power, social and personal.
Murray was one of the original psychologists to look into human needs. He developed a system of needs Murray's system of needs in which he identified and labeled needs that he believed were universal in nature for all humans. In all he came up with 20 needs. These needs positively correlate with the Big Five personality traits 
McClelland expanded on Murray's need theory. His theory focuses more on human needs and the effect that they have in a work environment. The three main components of his need theory are need for affiliation, need for achievement, and need for power.
How needs are measured
The Thematic Apperception Test has a purpose of revealing a person's drives, emotions, wants and needs by having them describe a story using a set of cards they are given. The test reveals a person's true wants and needs by the way they tell the story. A psychologist can interpret what their story means and can reveal certain aspects of subject's personality that they don't want to discuss or that they are unconscious of.
nPow is part of McClelland's acquired needs theory . People who exhibit nPow tendencies are most satisfied by seeing their environment move in a certain direction, due to their involvements. Individuals who are high in nPow have a desire to have an impact on others. They also tend to be more argumentative, assertive in group discussions, and likely to hold a position in which they have control over others. Most corporate leaders seek high level positions so as to control the direction in which their company is moving. A more specific individual who may be known to exhibit a high need for power is Nelson Mandela. He uses this influence to bring to light social issues in order to further his desire for peace and equality on earth. When someone high in nPow feels powerless or not in control of a situation, they are more likely to be frustrated. There is a difference in sexes in regard to how nPow is expressed. Men who have a high need for power, compared to women, tend to be more impulsive, aggressive, and engage in riskier behaviors. While men with more N-Pow show high levels of aggression, drink heavily, act in sexually exploitative manner, and participate in competitive sports, women channel their N-Pow in a more socially acceptable and responsible manner, being more concerned and caring.
Individuals with a high need for power exhibit a number of characteristics. These individuals tend to be more argumentative. Often elected to political offices; these individuals are also more assertive when a part of in-group discussions. They are known for displaying risk-taking behavior and they also tend to own more prestigious possessions such as expensive cars and credit cards.
For positions in which a person has control or power over others it is best if they are high in nPow compared to nAff or nAch. A good example of this is found in one of McClelland's studies. There was a man who was a sales manager for a corporation and who labeled himself as high in nPow. However, based on a questionnaire and views of co-workers he was found to be high in nAch. Conversely, he scored low on nPow. His co-workers complained that he was poorly organized, never rewarded them for work well-done, and did not have a positive impact on those working below him. This same man had done very well as a salesman before, but that is because nAch fits that position well and has a very low need for power 
Sharon Jenkins found in her research study that women who were involved in relational power jobs felt more satisfaction when it came to interpersonal power. Jenkins also found women who were involved with a relational power job would often have increases in need for power with time. Women who have high n Power are likely to stay in power related jobs 
In Leonard H. Chusmir's research, need for power was evaluated by looking at gender differences. Chusmir found that women had a higher need for power socialized power and less of a need to have personal power. This shows that women feel they need to have power in social situations and not necessarily in personal situations.
Pros and cons
There are both positive and negative aspects in regard to the need for power. Being argumentative can be perceived as an ideal expression of one’s opinion; although it can also create threatening environments for those of a more compliant nature. Having an assertive manner in group discussions can make others feel as though one is dominating a discussion within the group. However, this individual may have a profound impact on the group’s progress by assisting in accomplishing tasks more efficiently. Participating in risk-taking behavior can allow an individual to experience more radical events in their life, but sometimes risk-taking behavior can lead to undesirable consequences. Owning luxurious items tends to be costly, even though these possessions may make one feel good about themselves and their lives.
Other parts of the theory
Need for achievement
Murray defined need for achievement as the attempt to overcome obstacles. Need for achievement (nAch) was defined by McClelland as the motive to strive for success in particular situations in which his/her performance would be looked at against some type of standard. McClelland used the Thematic Apperception Test in order to test this part of his theory. He would show people four pictures and ask people to write a story regarding these pictures. Based on his/her story, McClelland would be able to determine what type of achievement a person strived.
Need for affiliation
Murray believed need for affiliation was a trait that was very strong in most people, especially in stressful situations. Murray believed that when people were put into a stressful situation, people were more likely to feel less stress if another person was present. In McClelland’s research, he found that people who had need for affiliation were often unpopular tried to avoid interpersonal conflicts because they have levels of anxiety about if others will accept them.
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