A
histogram is a graphical representation of the
distribution of numerical data. It is an estimate of the
probability distribution of a
continuous variable (quantitative variable) and was first introduced by
Karl Pearson. To construct a histogram, the first step is to "
bin" the range of values—that is, divide the entire range of values into a series of intervals—and then count how many values fall into each interval. The bins are usually specified as consecutive, non-overlapping
intervals of a variable. The bins (intervals) must be adjacent, and are usually equal size.