A letter value display describes the distributional shape of data (symmetry, heavy-tailedness) by pairs of numbers from the sorted data.
To properly analyze and understand results of letter values, you should be familiar with the following terms and concepts:
If you are not familiar with these terms and concepts, you are advised to consult with a statistician. Failure to understand and properly apply letter values may result in drawing erroneous conclusions from your data. Additionally, you may want to consult the following references:
- Hoaglin, D. C., Mosteller, F., and Tukey, J. W. (eds.). 1983. Understanding Robust and Exploratory Data Analysis. New York: John Wiley & Sons.
- Hoaglin, D. C., Mosteller, F., and Tukey, J. W. (eds.). 1985. Exploring Data Tables, Trends, and Shapes. New York: John Wiley & Sons.
- Mosteller, F. and Tukey, J. W. 1977. Data Analysis and Regression. Cambridge, MA: Addison-Wesley.
- Tukey, J. W. 1977. Exploratory Data Analysis. Cambridge, MA: Addison-Wesley.
- Velleman, P. F. and Hoaglin, D. C. 1981. Applications, Basics, and Computing of Exploratory Data Analysis. Duxbury Press.