The mean, also known as an arithmetic average, is calculated by adding the sum of all scores and dividing it by the total number of scores. For example, if you want to find the mean--or average--age of a group of people, you must first add all their ages together. Thus, if the ages within a group are 15, 19, 25, 33, 45 and 50, your total number is 187. You then take this number and divide it by six--the number of people in the group--and you arrive at 31.17. Therefore, the mean age of this group is 31.17 years.
The mean is so important in psychological research because it allows researchers to organize and summarize an immense amount of data into values that are more comprehensible. Furthermore, it allows psychologists to scientifically analyze their data, reducing the opportunity for the results to be skewed by biases or interpretation. Finally, it provides clear data that other psychological researchers can build on for their own studies and statistics that the general public can understand.
Psychological researchers rely on the scientific method to objectively study the mind and body. The scientific method of research involves four steps, with all but step two commonly using measures of mean. First, a problem is conceptualized and a hypothesis formed. Quite often this is done through observing the summarized data--or measures of central tendency---of other researchers. Second, data is collected through various procedures. Third, the data is analyzed through statistical methods with measures of mean being the most commonly used. Fourth, conclusions are drawn based on the statistical findings in step three.
The mean can be strongly influenced by extreme scores, often resulting in misleading statistics. For example, the mean age of a group of people who are 15, 16, 17, 18, 19 and 80 is 27.5. This number is significantly higher than the ages of the majority and much lower than the oldest person in the group. Thus, to say the mean age is 27.5 provides an inadequate representation of the data.
It is appropriate to use a mean score as a measure of central tendency when the quantitative data you are analyzing forms a normal distribution or bell curve--that is, when most of the scores are relatively similar and a few fall slightly above and slightly below the average. Data that consist of a few highly extreme or unusual scores will not be adequately represented using this measure. In this case, a psychological researcher would turn to one of the two lesser used measures--mode or median--as a supplementary or replacement measure.