Bar Chart: Definition
A Bar Chart or a Bar Graph can show visually the size of the levels or Categories of a Qualitative Variable. Therefore, visually, it is easier to compare these categories and to extract useful results.
Bar Chart: Bars
Each bar can represent a Main Category as well its subcategories. Subcategories can either be presented one upon another on a bar, or side by side, always grouped by a main category. Space exists between the main categories. This space signifies that a Discrete (non-continuous) Variable is displayed. This is the main visual difference with a Histogram.
These bars can be either Horizontal based on Y axis or Vertical based on X axis. One of the axis will display the names or levels of the Categories, and the other axis will display the Discrete values of the variable. The Height of each bar is relative to the size of each Main category or one of its subcategories.
Bar Chart: A little History
A type of Bar chart was used first time by Nicole Oresme (14th century) and by Sir Isaac Newton (17th century) to present visually the Laws of Motion: velocity and Acceleration per time units. The 17th century, Joseph Priestley presented a timetable of Biographies that was a type of bar Graph. William Playfair (17th century) presented a Bar chart that is the same type of Bar chart that we use today. In this Bar chart, the imports and exports from various countries from and to Scotland was presented for one year.
Bar Chart: Horizontal vs Vertical bars
There are two main types of Bar chart based on how its bars are positioned:
i) Horizontal Bar Chart: Its bars are positioned horizontally, parallel to X axis.
ii) Vertical Bar Chart or Column Bar Chart: Its bars are positioned vertically (Standing), parallel to Y axis.
Bar Chart: Subcategories presentation
The type of a Bar chart can differ based on how a Main Category as well its subcategories are visually presented:
i) Stacked Bar Chart: The subcategories of a Main category can presented in a single bar, one upon another, like Legos. Then, the size/height of the bar shows the total size of the Main Category. It can present either the normal size (f) or the Relative size (f%) of each subcategory. If relative size is presented, then the total size of the bar/Main category is equal to the value of 100%.
ii) One front of other according to its height: A Bar can be presented in front of another bar in an ascending order based on their height/size. Then, the difference between sub-categories is visually presented e.g. by different colors. The main categories are presented with space between them.
iii) Side by Side: The sub-categories of a Main Category are presented side by side, grouped under this main Category. The main Categories/grouped bars are presented with space between them.
Vertical Bar Chart: Example Ι: Side by Side
In this Bar graph, the size of 470 cats -big cats (Red Bars) versus small cats (Blue Bars)- and its color -Black, White, Brown, two colors, and Multicolor- is compared (fake data):
i) The Multicolor category is the highest color category of cats (190) which is represented by 100 Small cats and 90 Big cats.
ii) The Big Brown cats is the least represented category.
Horizontal Stacked Bar Chart: Example ΙΙ
The following Horizontal Stacked Bar Chart presents the number of Biological (Orange bar) versus of Non-biological (Deep Blue bar) bottle of wines that were sold in a region for four months -from January to April (fake data):
i) The total number of bottle of wines that were sold in February, is the highest one between these four months.
ii) The biological bottle of wines were sold most in Mars and least in April.
Horizontal Stacked (100%) Bar Chart: Example ΙII
The following Horizontal Stacked (%) Bar Chart compares the % quantity of Green (Green bars) versus Other type of Tea (Light Blue bars) for Cold and Hot Tea cups that were ordered in a Restaurant e.g. in August (fake data):
i) Almost 40% of the clients ordered a Green Tea and 60% ordered other type of Tea when they ordered a Cold Tea cup.
ii) 20% of the clients ordered a Green Tea and 80% ordered other type of Tea when they ordered a Hot Tea cup.
iii) The total quantity of Green Tea cups that was ordered cannot be compared with the total quantity of Other type of Tea cups that was ordered because both bars are expressed in %.
iv) For example, clients may ordered 200 Hot Green Tea cups versus 800 Hot Other Tea cups and they may have ordered 4 Cold Green Tea cups versus 6 Cold Other Tea cups.