The way a statistic is calculated may be more
important than the result it produces. Recently an
example showed up when some statistics were being checked
using Excel on results produced with SAS, specifically
with the calculation of a first and third quartile, also
known as the 25 For the data 1, 2, 3, 4, 5, 6, 7 and 8 the following
results are calculated for the 25
Why the difference? There actually is no standard for the calculation of percentile and it does depend on what a statistician is looking for. SAS has six methods of calculating the percentile, the two common ones being:
Excel, S-Plus and StarOffice Calc by comparison uses a different method, specifically:
Among the major statistical software packages only Excel, S-Plus and StarOffice Calc use this method. For those using Minitab or SPSS they use the SAS Method 4 for their calculation. The moral of this example is that you should know how your software calculates a statistic before blindly reporting the result. |
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________________________________ Updated December 15, 2003 |