.

In the Box and whisker plot, the central box represents the values from the lower to upper quartile (25 to 

75 percentile).  The middle line represents the median.  The horizontal line extends from the minimum to 

the maximum value, excluding outside and far out values, which are displayed as separate points. 

An  outside value is defined as a value that is smaller than the lower quartile minus 1.5 times the 

interquartile range, or larger than the upper quartile plus 1.5 times the interquartile range (inner fences). 

These values are plotted with a square marker. 

A far out value is defined as a value that is smaller than the lower quartile minus 3 times the interquartile 

range, or larger than the upper quartile plus 3 times the interquartile range (outer fences). These values 

are plotted using a marker drawn in the  warning  color (see p. Error! Bookmark not defined.). 

As an option, you may select to plot all individual data points.  This enables you to obtain a diagram 

representing a statistical summary of the data without the disadvantage of concealing the real data. 

When you click an individual observation in the graph, the corresponding case is identified in a popup 

window (see also Select variable for case identification menu command, p. 41).  If you double click an 

observation, the spreadsheet window will open with the corresponding case highlighted.  If the value is an 

outlier, you can exclude the value or the entire case from further statistical analysis by selecting the value 

Exclude command in the Tools menu (see p. 37). 

Presentation of results 

The description of the data in the text or table may be complemented by a graphical representation of the 

data: a histogram, cumulative distribution or box and whisker plot.  The histogram is not very effective to 

display location and spread.  The cumulative distribution has the advantage that it makes it easy to 

estimate the median (or other percentile) by reading off the horizontal value at which the curve attains 50% 

(or other percentage) (Moses, 1987). Secondly, the plot can contain the individual observations 

(cumulative dot plot).  Finally, the box and whisker plot may be preferable because it can combine a 

display of all the data together with a statistical summary. 

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