Читать книгу Statistics and Probability with Applications for Engineers and Scientists Using MINITAB, R and JMP - Bhisham C. Gupta, Irwin Guttman - Страница 85

The average of the lower and upper limits of a class (bin) is called the class midpoint or class mark.

To compute the measures of centrality and dispersion for a grouped data, each measurement in a given class is approximated by its midpoint. Thus, the measures computed from grouped data are only approximate values of measurements obtained from the original data. The actual approximation, of course, depends on the class width. Thus, in certain cases, the approximate values may be very close to the actual values, and in other cases, they may be very far apart. A word of caution: measurements obtained from grouped data should only be used when it is not possible to retrieve the original data.