is an accurate 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. It differs from a bar graph
, in the sense that a bar graph relates two variables, but a histogram relates only one. To construct a histogram, the first step is to "bin
" (or "bucket
") 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 often (but are not required to be) of equal size.
If the bins are of equal size, a rectangle is erected over the bin with height proportional to the frequency
—the number of cases in each bin. A histogram may also be normalized
to display "relative" frequencies. It then shows the proportion of cases that fall into each of several categories
, with the sum of the heights equaling 1. Read more...