Tukey boxplots divide data into 7 groups, the middle 50%, and three lower and higher groupings: within the whisker, near outliers and far outliers, respectively. Symbols for values below the first quartile (Q1) are plotted as increasingly larger circles, while symbols for values above the third quartile are plotted as increasingly larger squares, a ‘+’ is used to plot the data falling in the middle 50%. For the higher groupings, the whisker contains values >Q3 and <(Q3 + 1.5 * HW)
, where HW = (Q3 - Q1)
, the interquartile range; near outliers lie between (Q3 + 1.5 * HW)
and (Q3 + 3 * HW)
; and far outliers have values >(Q3 + 3 * HW)
. For the lower groupings the group boundaries, fences, fall similarly spaced below Q1. The computation of the fences used to subdivide the data may be carried out following a logarithmic transformation of the data, set logz = TRUE
.
A summary table of the values of the symbol intervals, the number of values plotting as each symbol, and symbol shapes, sizes and colours is displayed on the current device.
If zlab
and main
are undefined a default a map title is generated by appending the input variable name text string to "EDA Tukey Boxplot-Based Map for "
. If no map title is required set zlab = ""
, and if some user defined map title is required it should be defined in main
, e.g. main = "Map Title Text"
.
If the grey-scale option is chosen the symbols are plotted 100% black for the far outliers, 85% black for the near outliers, 70% black for values within the whiskers, and 60% black for values falling within the middle 50% of the data.
The default colours, symcolr = c(25, 22, 20, 13, 6, 4, 1)
, are selected from the rainbow(36)
pallette, and alternate colour schemes need to be selected from the same palette. See display.rainbow
for the available colours. It is essential that 7 colours be provided, e.g., symcolr = c(27, 24, 22, 12, 5, 3, 36)
, if exactly 7 are not provided the default colours will be displayed.