ABSTRACT
This chapter examines summation notation, central tendency, and dispersion. Many areas of statistics, including many methods of descriptive and inferential statistics, require the use of summation notation. The chapter considers the three most popular indices, known as measures of central tendency. Although other indices exist, the most popular ones are the mode, the median, and the mean. The simplest method to use for measuring central tendency is the mode. The general characteristics of the median are as follows. First, the median is not influenced by extreme scores. A second characteristic is that the median is not a function of all of the scores. The final measure of central tendency to be considered is the mean, also known as the arithmetic mean or average. The mode is the only appropriate measure for nominal data. The median and mode are both appropriate for ordinal data. All three measures (mode, median, and mean) are appropriate for interval and ratio data.
