Numerical Description of Data
The graphic procedures described in the last chapter help us to visualize the pattern of a data set. To obtain a more objective summary description and a comparison of data sets, we must go one step further and formulate quantitative measures for important aspects such as the location of center of the data and the amount of variability present in the data. To effectively present the ideas and associated formulas, it is convenient to represent a data set by symbols to prevent the discussion from becoming anchored to a specific set of numbers. A data set consists of a number of measurements symbolically represented by \(x_1, x_2, \cdots, x_n\). The last subscript n denotes the number of measurements in the data and \(x_1, x_2, \cdots,\) represents the first observation, the second observation and so on.