Bar graphs are used to compare an amount of a variable at particular times or points, or to compare the amount of one variable to another. Bar graphs are less effective in emphasizing the trend in a variable over time. They may be horizontally or vertically oriented. The virtue of bar graphs is their simplicity, so they should be as uncluttered as possible.

Good Example

Poor Example

• Use as few bars as necessary with a maximum of six different bars.
• Emphasize one aspect of the data by changing a specific bar’s color or texture.
• Control bars are usually left unfilled to stand apart from experimental variables or colored white for color graphs.
• Bars should be wider than the spaces between them. All bars should be of equal width, and all spaces including the space between the axis and the first bar, should be of equal width. Bars should be neither very thin nor very wide.
• With groups of bars, the groups should be separated by a space, but no space is necessary between the bars of a group. The space between the groups of bars should be about the width of one bar or less.
• Data values should not be written either within the bar or outside it. If exact values are important, the data should be presented as a table. If bars are labeled with values, don’t use either tick marks or grid lines.
• Baseline need not be drawn. It is not an axis. If it is drawn, it does not have tick marks.
• Use the same fill color for all bars in single data set.
• Use different fill colors for positive and negative values.
• For single bars, labels are centered below each bar.
• For groups of bars, individual bars can be labeled. Group labels can be centered below the individual bar labels for vertical bar graphs or placed to the left of the individual bar labels in horizontal bar graphs. The groups can be labeled and the bars can be distinguished by shading or patterns. Lettering in individual column labels is smaller than lettering in the group labels.
• The longest bar (or its error bar) should reach nearly to the end of the graph.

• Use 5 or fewer segments per bar or bars per cluster.
• Use darkest or densest fills for segments at baseline (or left side) and lighter fills as segments rise up bar (or on right side).
• Display values over, next to or inside tops of bars when precise values are significant.
• Add connecting lines between bar segments to facilitate comparisons.