When the effects are significant, the means must then be examined in order to determine the nature of the effects. For example, in the preceding analysis, Gestalt and Behavior Therapy were the most effective in terms of mean improvement. In the case of significant effects, a graphical presentation of the means can sometimes assist in analysis. First, a review of the sampling distribution is necessary. If you have difficulty with this summary, please go back and read the more detailed chapter on the sampling distribution.
Sample statistics are numbers which describe the sample.
Probability models exist in a theoretical world where complete information is unavailable. As such, they can never be known except in the mind of the mathematical statistician. If an infinite number of infinitely precise scores were taken, the resulting distribution would be a probability model of the population. Population models are characterized by parameters. Two common parameters are and .