To calculate the symmetry plot, Minitab does the following:
- Sorts the n values in ascending order.
- Calculates the median.
- Creates ordered pairs of values (a, b) in the following way:
- The first pair (a, b) consists of the nearest value above the median (a) and the nearest value below the median (b).
- The second pair consists of the second nearest value above the median and the second nearest value below the median.
- Continue this pattern to form a total of n / 2 (when n is even) or (n – 1) / 2 (when n is odd) ordered pairs of values.
- Calculates the plot's distance values for each ordered pair of values. The x-coordinate is the distance between a and the median, and the y-coordinate is the distance between b and the median.
- Plots the ordered pairs of distances.
From left to right on the symmetry plot, both coordinates increase because both values in each ordered pair move farther from the median.
Minitab also displays a histogram to provide an alternate view of the distribution.