Box plot

A statistical graph that summarizes a dataset with a box spanning the first and third quartiles, a median line, and often whiskers and outlier markers.

Median: The middle value of an ordered dataset, or the midpoint between its two middle values. The line inside the box marks the dataset’s median.
Tukey's fences: A rule that flags values below Q1 − 1.5 IQR or above Q3 + 1.5 IQR as potential outliers. This common rule determines which points appear beyond the whiskers.
Grouped box plot: A display of box plots for multiple groups, aligned on a shared scale. Side-by-side boxes compare medians, spreads, and possible outliers across groups.
Histogram: A graph that groups numerical observations into bins and displays their frequencies. A histogram shows distribution shape that quartiles and whiskers can obscure.
Quartile: A value dividing ordered data into four groups with approximately equal numbers of observations. The box edges mark the first and third quartiles.
Whisker (statistics): A line extending from a box plot’s box to a specified endpoint in the data. Whisker endpoints may show the most extreme non-outlying observations.
Notched box plot: A box plot with a narrowing around the median that approximates a confidence interval for it. The notch offers a rough visual comparison of group medians.
Empirical cumulative distribution function: A step function giving the proportion of sample observations less than or equal to each value. It preserves the full ordered distribution rather than only selected quantiles.
Interquartile range: The difference between the third quartile and the first quartile, measuring the spread of the middle half of data. The box’s length represents this central spread.
Modified box plot: A box plot whose whiskers typically end at the most extreme values within Tukey’s fences, with outliers plotted separately. This variant makes the outlier rule explicit in the display.

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