What is a Stem-and-Leaf Plot?
A stem-and-leaf plot (or stemplot) displays quantitative data in a semi-tabular format where each value is split into a stem (typically the leading digit(s)) and a leaf (typically the final digit). For example, the number 73 is split into stem=7 and leaf=3.
What makes stem-and-leaf plots unique is that they preserve every original data value while simultaneously showing the distribution shape — essentially a hybrid between a table and a histogram. They are particularly popular in educational settings for teaching descriptive statistics, and remain useful for quality control dashboards and quick exploratory analysis of small datasets.
For larger datasets (100+ values), the distribution shape remains visible but individual leaves become less meaningful. In those cases, a histogram may be more practical, though the stem-and-leaf still provides an audit trail of exact values.
Frequently Asked Questions
When should I use a stem-and-leaf plot instead of a histogram?
What do the stem and leaf represent?
Computation Method
- Quartiles are calculated using linear interpolation (method 7 from Hyndman & Fan, 1996), consistent with Python's NumPy and pandas defaults.
- Outlier detection uses the Tukey fences method: lower fence = Q1 − 1.5 × IQR, upper fence = Q3 + 1.5 × IQR.
- Chart scaling caps the display axis at the upper fence value so the visualization remains clear even when extreme outliers are present.
References
- Hyndman, R. J. & Fan, Y. (1996). “Sample Quantiles in Statistical Packages.” The American Statistician, 50(4), 361–365.
- Tukey, J. W. (1977). Exploratory Data Analysis. Addison-Wesley.