st: -stripplot- updated on SSC

["Nick Cox" <n.j.cox@durham.ac.uk>]

Thanks to the ever-active Kit Baum, -stripplot- has been updated on SSC (again). Use -ssc- or -adoupdate- to install or update if desired. Stata 8.2 or higher is required. 

-stripplot- for a while has had a -box- option. Now you can add whiskers as desired, at least so long as that desire is matched by my prejudices. A request to add whiskers was made by Ronán Conroy.

The help explains the matter: 

box specifies that boxes be added showing medians and quartiles.  Box information is
        calculated using egen, median() and egen, pctile().  box(box_options) may be
        used to specify options of twoway rbar to control the appearance of the box. For
        example, box(bfcolor(eltgreen)) specifies eltgreen as the box fill colour.  The
        defaults are bcolor(none) barwidth(0.4). Note that the length of each box is the
        interquartile range or IQR.

        iqr[(#)] specifies that spikes are to be added to boxes that extend as far as
        the largest or smallest value within # IQR of the upper or lower quartile. Plain
        iqr without argument yields a default of 1.5 for #.

        pctile(#) specifies that spikes are to be added to boxes that extend as far as
        the # and 100 - # percentiles.

        whiskers() specifies options of twoway rspike that may be used to modify the
        appearance of spikes added to boxes.

        iqr, iqr(), pctile() and whiskers() have no effect without box or box(). iqr or
        iqr() may not be combined with pctile().

At the same time, please note that -stripplot- does not aim or pretend to clone all the functionality of -graph box- or -graph hbox-. 

The help also adds some historical information that may be of some interest. 

    Box plots in widely current forms
    are best known through the work of Tukey (1972, 1977). Similar ideas go back much
    further.  Cox (2009) gives various references. Bibby (1986, pp.56, 59) gave even
    earlier references to their use by A.L. Bowley in his lectures about 1897 and to his
    recommendation (Bowley, 1910, p.62) to use minimum and maximum and 10, 25, 50, 75
    and 90% points as a basis for graphical summary.

So, a belated but deferential nod in the direction of Sir Arthur Lyon Bowley.  

The full references are naturally given in the help. 

Nick 
n.j.cox@durham.ac.uk 



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