Bar graphs

Title

Titles should be as short as possible. Unless necessary to understand the figure, words which describe a method or explain a result in detail should be avoided. The title should be written as a sentence, without using title cases, eg. "Effect of Drug A in Mice" should be "Effect of drug A in mice".

Y-axis

The y-axis title should be simple, and the unit written in parenthesis. Avoid describing the unit in the title, eg. "Milligrams of protein" is better written as "Protein (mg)". For the y-axis scale, do not use more than seven numbers. For example, for results up to 100%, a gradation should be used every 20% instead of 10%.

The y-axis scale start:

Choose an appropriate scale for your data. The y-axis does not always start at 0. For example, if your data starts at 80%, consider using 70% as a starting value for the y-axis. Leave one-gradation above, and occasionally below, your highest and lowest value, respectively.

X-axis

The x-axis should also have a simple title with units. Timelines should be in increasing chronological order, from past to most recent time. For individual categories, group data according to the most significant variable. For example, in an experiment evaluating apoptosis in cells 0, 6 and 12 hours after treatment with drug A or B, if the effect of each drug on apoptosis is emphasized, data should first be grouped by drug, then treatment time. However, if a comparison of drugs A and B at each time point is emphasized, data should be grouped by treatment time, then drug.

Bar formatting

Depending on the journal, bars can be in color or in black in white. Please refer to journal guidelines. For black and white figures, choose contrasting shades of gray, including black. Avoid using textures, such as hashed lines, dots, motifs, etc.

For multiple data in one category, space out bars by a few pixels. In Excel, under "Format Data Series" and "Options", choose an "Overlap" of approximately -20.

Background and gridlines

A graph should have a minimum of graphic decorations. Therefore, many figures in journals do not include gridlines nor background. However, if gridlines are necessary, they must be kept as light as possible.

Vertical or Horizontal?

For results with more than 8-10 categories, bar graphs are sometimes better represented horizontally, as shown in the example below.

Also note that categories (Hospitals) are classified by increasing physical test scores because the study focused more on the physical than mental condition of patients. Classification of data is also important to focus results.

Stacked bar graphs

Stacked bar graphs should be used with care. Bar height comparisons are easiest with the bottom data, but may become more difficult with bars stacked higher on the column. This is especially true data which do not have great variation.

Common mistakes to avoid

• No space between axis title and unit in parenthesis
• Use of background color
• Bars which are either too cramped or too spaced out
• Starting the y-axis scale at zero when data starts at a significantly higher value
• Different font and font sizes for axis titles, scales, and data