Definition and Purpose of Histograms

A histogram is a visual representation of data distribution that uses bars to show the frequency of data in various intervals.
It is used to obtain a rough understanding of the probability distribution of a given variable.
Histograms provide a visual interpretation of numerical data by indicating the number of data points that fall within a specified range of values.

Creating a Histogram

To create 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—then count how many data points fall into each interval.
The x-axis is divided into bins, and each bar in a histogram represents the tabulated frequency at each bin.
The variable being measured is plotted along the x-axis, and the frequency is plotted along the y-axis.
The bins (intervals) should be consecutive, adjacent, and non-overlapping.

The height of each bar correlates with its frequency.
By looking at a histogram, one can learn the center, spread and shape of the data.
A unimodal distribution has one peak; a bimodal distribution has two peaks; a multimodal distribution has more than two peaks.
Data can also be symmetric, left-skewed, or right-skewed.

Unlike a bar chart, a histogram does not have gaps between columns, unless there is a class interval that contains no data.
A bar chart is used for comparing different categories of nominal or ordinal data, while a histogram is used for continuous or interval data.