Difference Between Bar Graph and Histogram

Bar Graph vs Histogram

In statistics, summarizing and presentation of the data is important. It can be done either numerically using descriptive measures or graphically using the pie graphs, bar graphs, and many other graphical representation methods.

What is a Bar Graph?

Bar graph is one of the main graphical representation methods in statistics. It is used to display distinct values of the qualitative data on a horizontal axis and the relative frequencies (or frequencies or percents) of those values on a vertical axis. A bar with its height/ length proportional to the relative frequency represents each distinct value, and the bars are positioned in a way that they do not touch each other. A bar graph with the above configuration is the most common and is known as a vertical bar graph or a column graph. But it is also possible to interchange the axes; in that case the bars are horizontal.

The bar graph was first used in the 1786 book “The Commercial and Political Atlas” by William Playfair. Since then bar graph has become one of the most important tools in representing categorical data. Use of bar graphs can be extended to represent more complex categorical data, such as time developing variables (election response), grouped data, and more.

What is a Histogram?

The histogram is another important graphical representation of data, and it can be considered as a development from the bar graph. In a histogram, the classes of the quantitative data are displayed on the horizontal axis, and the frequency (or relative frequency or percents) of the classes are displayed on the y axis. A vertical bar usually represents the frequency (or relative frequency or percents) of the class whose height is equal to its magnitude. Unlike the ordinary bar graphs, the bars are positioned to touch each other.

The variable in the X-axis-axis can be either single value grouped or limit grouped. For single-value grouping, distinct values of the observations are used to label the bars, with each such value centered below its bar. For limit grouping or cut point grouping, lower class limits (or, equivalently, lower class cut points) are used to label the bars. Class marks or class midpoints centered under the bars can also be used.

One of the major differences lies in the variable used in the X-axis-axis. In the histogram, the variable is a quantitative variable and can be either continuous or discrete. And it can be used to represent density information about the datasets. In this case, the intervals used on the x-axis may vary from one to another, and on the y axis, the frequency density is marked. If the interval of the X- axis is 1, then the histogram is equal to the relative frequency plot.

What is the difference between Bar Graph and Histogram?

• First and foremost, a histogram is a development from the bar graph, but it is not identical to a bar graph. Histograms are a type of bar graphs, but bar graphs definitely are not histograms.

• Bar graphs are used to plot categorical or qualitative data while histograms are used to plot quantitative data with the ranges of the data grouped into bins or intervals.

• Bar graphs are used to compare variables while histograms are used to show distributions of variables

• Bar graphs have spaces between two bars while histograms have no spaces between the bars. (The reason is that the x- axis in bar graphs are discrete categorical values while, in histograms, it is either discrete or continuous quantitative).

• Histograms are used to illustrate the density of a variable in intervals; in this case the area of the bar represents the frequency of the variable.