Box plots is a quick way of examining one or more sets of data graphically. In statistics, a box plot is a convenient way of depicting groups of numerical data through their quartiles. Box plots may also have lines extending vertically from the boxes (whiskers) indicating variability outside the upper and lower quartiles, which brings up the terms box-and-whisker plot and box-and-whisker diagram. Outliers may be plotted as individual points.
Box plots are non-parametric: they display variation in samples of a statistical population without making any assumptions about the underlying statistical distribution. The spacings between the different parts of the box indicate the degree of dispersion (spread) and skewness in the data and show outliers. In addition to the points themselves, they allow one to visually estimate various L-estimators, notably the interquartile range, midhinge, range, and mid-range. Box plots can be drawn either horizontally or vertically. Box plots received their name from the box in the middle. But the ends of the whiskers can represent several possible alternative values, among them: the minimum and maximum of all the data, one standard deviation above and below the mean of the data, the 1st percentile and 99th percentile, the 2nd percentile and the 98th percentile, etc.
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