Fifteen STC members and non-members gathered on November 19 to hear the webinar “How to Avoid Common Graphical Mistakes” by Naomi B. Robbins. The session addressed techniques for improving graphs, charts, and tables. The topics and some important points included:
Understand human perception and our ability to decode graphics:
- Angles on pie chart wedges are difficult to judge.
- Lengths should have a common baseline.
- A common scale is required for more accurate interpretation of data.
Avoid misleading your audience:
- Don’t use evenly spaced tick marks for uneven intervals.
- Use consistent colors, scales, and other elements for groups of charts.
- Bar graphs require a zero baseline, dot plots do not.
Make the data stand out:
- De-emphasize non-data elements.
- Avoid 3-D charts–they are difficult to read.
- Make grid lines barely perceptable.
Eliminate problems with tick marks and labels:
- Don’t overdo the number of tick marks and labels.
- Proofread graphs.
- Tick marks should use logical values and intervals.
- Round data.
- Do not overuse rules and grids.
- Right-justify numbers.
During the presentation, Naomi provided many examples of poor graphs and charts to emphasize the points she made. She also redrew many of them using her recommendations. The corrected charts presented a striking difference in accurately representing the data, making it easier for readers to interpret the information correctly.
Namoi B. Robbins is the author of the book “Creating More Effective Graphs.” Her Web site is at www.nbr-graphs.com, and she provides some great information on the page www.nbr.-graphs.com/trainframe.htm (click on the link How to Draw Some Useful Charts Not on Excel Menus).Â Naomi also recommends the following books:Â “Excel Charts” by John Walkenbach, “The Elements of Graphing Data” by William S. Cleveland, and “Visualizing Data” by William S. Cleveland.