Bar charts are often primarily used for displaying the quantities of qualitative or categorical data (e.g. age group, religious affiliation), although they can also be used for quantitative data if the number of unique scores in the data set is not large.
A bar chart plots the number of times a particular value or category occurs in a data set, with the length of the bar representing the number of observations with that score or in that category (e.g. the number of people in a sample falling into a given income or ethnic group). While one axis represents the different (nominal) categories, the other axis can represent any measurement unit: relative frequency, raw count, percent, or whatever else is appropriate for the situation. Graphing by percent is most common.
Bar charts can be displayed horizontally or vertically (which are sometimes referred to as column charts) and they are drawn with a gap between the bars, whereas the bars of a histogram are drawn immediately next to each other.
Investment by area of impact
This example takes a close look at a vertical bar graph and breaks down several changes which transform it into an easier to interpret, more communicative horizontal bar graph (shown above).
Source: Cole Nussbaumer http://www.storytellingwithdata.com/2012/10/my-penchant-for-horizontal-b...
Runs scored by national league division
These examples are simple bar and column charts prepared in Excel. Default formatting in Excel was adjusted to soften the gridlines and data labels to make the data and message stand out.
Advice for CHOOSING this option (tips and traps)
People are most accurate at judging length, thus making bar charts one of the best choices for communicating data. They are fairly well understood and easily interpreted.
Advice for USING this option (tips and traps)
Order the data in some meaningful way, usually greatest to least. Only place data on the chart that is for the comparison. Too many columns or bars can oversaturate the chart and become confusing. To solve this, prepare multiple comparative charts for different variables.
Bar Charts and Histograms: Clear explanation on how to make histograms and bar charts (with a clear 9-minute video – you can flip through different chapters if you find it too long).
Other ways to compare sets of values
Presenting a frequency distribution of quantitative data in a graphical way.
Providing a way to communicate complicated data sets quickly and easily.
Using a target line to show progress to date, often with levels of performance graphed in the background.
Deviation bar graph
Aligning two bar graphs along their spine to compare the shape of their data sets.
Plotting two or more dots on a single line for each category being compared.
Positioning several small graphs with the same scale in a row for easy comparison.
Nussbaumer, C. (2012). storytelling with data: my penchant for horizontal bar graphs. Retrieved September 2014, from http://www.storytellingwithdata.com/2012/10/my-penchant-for-horizontal-b...
School of Psychology, University of New England (2000). Histograms and Bar charts. In: Chapter 4 Analysing the data (Research Options and Statistics course): http://www.une.edu.au/WebStat/unit_materials/c4_descriptive_statistics/histograms_barcharts.html
Valery J Easton and John H. McColl (1997). Statistics Glossary: http://www.stats.gla.ac.uk/steps/glossary/presenting_data.html#bar