|   | DATA MINING Desktop Survival Guide by Graham Williams |   | |||
| Box Plot | 
 over the whole population, as we
can see from the Summary option's Summary check
box). The top and bottom extents of the box (
 over the whole population, as we
can see from the Summary option's Summary check
box). The top and bottom extents of the box ( and
 and  respectively) identify the upper quartile (the third quartile or the
75th percentile) and the lower quartile (the first quartile and the
25th percentile). The extent of the box is known as the
interquartile range
(
respectively) identify the upper quartile (the third quartile or the
75th percentile) and the lower quartile (the first quartile and the
25th percentile). The extent of the box is known as the
interquartile range
( ). The
dashed lines extend to the maximum and minimum data points that are no
more than
). The
dashed lines extend to the maximum and minimum data points that are no
more than  times the interquartile range from the
median. Outliers (points further than
 times the interquartile range from the
median. Outliers (points further than  times the interquartile
range from the median) are then individually plotted (at 79, 81, 82,
83, and 90).  The mean
(38.62) is also displayed as the
asterisk.
 times the interquartile
range from the median) are then individually plotted (at 79, 81, 82,
83, and 90).  The mean
(38.62) is also displayed as the
asterisk.
The notches in the box, around the median, indicate a level of
confidence about the value of the median for the population in
general. It is useful in comparing the distributions, and in this
instance it allows us to say that all three distributions being
presented here have significantly different means. In particular we
can state that the positive cases (where  ) are older than
the negative cases (where
) are older than
the negative cases (where  ).
).
We note that the annotated box plot (as enable by checking the Annotate check box) does not attempt to place the annotations in any particularly optimal location, except a little below the point being annotated. They may be a little difficult to read at times. The user is at liberty to correct thus through replicating the plotting steps from the log window, but modifying the offsets in the display of the annotations.
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