Summarizing
Data:
Simple
Statistics:
THE SPREAD continued
Percentile Ranges
The most
common of these is the interquartile range, although even this
is a seldom-visited feature on the statistical map. It is used with
the median to give an idea of centrality and spread of skewed
or otherwise grossly non-normally-distributed variables. Measures of
training are often skewed enough to merit use of percentiles instead
of the mean and standard deviation. For example, weekly training in a
group of novice athletes might have a median of 5 and an
interquartile range of 3-12 hours/week.
Here's something challenging for the real lovers of numbers. The
mean ± SD encloses 68% of the data on average for a normally
distributed variable. So if you want to use a percentile range that
corresponds to the mean ± SD, what should it be? Answer:
16th-84th. If I had my way, this measure would replace the
interquartile range. We could call it the standard percentile
range…
We're right out on the horizon now. Let's get back to familiar
territory.
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Last updated 29 April 97