Psychologists often employ standardized personality, aptitude and intelligence tests. The controlled experiment allows a psychologist to test a hypothesis about the relationship of the two variables to see if there is a cause-effect relationship. For instance a survey in Cosmopolitan Magazine on premarital sex activity will probably not represent the general U.S. population but a subgroup of relatively affluent, young, white women. By comparing results of the experimental group to those of the control group the researcher can assess whether significant change occurred by the treatment. The double-blind procedure controls for this subject bias.
Most scores cluster around the center with lesser number of scores being higher or lower.
The MEAN is the average score calculated by adding up all the scores and dividing by the number of scores. The MODE is the score that occurs most frequently in a group of scores. The mean, median and mode do not coincide. It is computed as the square root of the average squared deviation from the mean. All measures of variance help experimenters interpret the significance of the data obtained in a set of scores.