1. PSY 1950 Graph Design December 8, 2008

4. Why graph? Exploratory data analysis –Usually raw data –Tukey: a good graph “forces us to notice what we never expected to see” –e.g., scatter plot, funnel plot –Design less important Communication –Usually summary statistics –“a picture is worth a thousand words” –e.g., line graphs, bar graphs –Design extremely important

7. Bar Graphs vs. Line Graphs Bar graphs –Convey position (i.e., bar height) Effective in conveying relative point values Ineffective for conveying interaction effects –X axis has nominal or ordinal scale Line graphs –Convey change in position (i.e., line slope) Ineffective in conveying relative point values Effective for conveying interaction effects –X axis has interval or ratio scale Okay for 2-level nominal scale

8. Values vs. Trends

9. Relevance Communication is most effective when neither to much nor too little information is presented Tufte (1983): “Maximize the data-ink ratio, within reason”, where data-ink ratio is the “proportion of a graphics ink devoted to the non-redundant display of data.”

10. Distracting Backgrounds

11. Appropriate Knowledge Communication requires prior knowledge of relevant concepts, jargon, and symbols

12. Jargon, Symbols

13. Concepts

14. Salience Attention is drawn to large perceptible differences Discriminability Two properties must differ by a large enough proportion or they will not be distinguished

15. Size

16. Proportion

17. Scale

18. Perceptual Organization People automatically group elements into units, with they then attend to and remember

20. Compatibility A message is easiest to understand if its form is compatible with its meaning

21. Color, Category Placement

22. Between vs. Within Subjects

23. Informative Changes People expect changes in properties to carry information

24. Capacity Limitations People have a limited capacity to retain and to process information and will not understand a message if too much information must be retained or processed

26. Placement is Key

27. Horizontal vs. Vertical Bars: Labels

28. Font Type http://www.surl.org/usabilitynews/32/font.asp

29. Font Type http://www.surl.org/usabilitynews/32/font.asp

30. Font Style ALL UPPERCASE TEXT IS HARDER TO READ than all lowercase text or Mixed Case Text Italicized text is harder to read than plain text Underlined text (e.g., pajamas) is harder to read than non-underlined text (e.g., pajamas)

31. Scatterplots

32. Example Zachs, J., & Tversky, B. (1999). Bars and lines: A study of graphic communication. Memory & Cognition, 27, 1073-1079.