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st: Interpreting summarize, detail
From
Syed Basher <[email protected]>
To
[email protected]
Subject
st: Interpreting summarize, detail
Date
Sat, 5 Feb 2011 22:09:05 -0800 (PST)
Hello all,
I am having some difficulty in interpreting the basic summary statistics.
Consider the following:
. sysuse auto
(1978 Automobile Data)
. summarize mpg, detail
Mileage (mpg)
-------------------------------------------------------------
Percentiles Smallest
1% 12 12
5% 14 12
10% 14 14 Obs 74
25% 18 14 Sum of Wgt. 74
50% 20 Mean 21.2973
Largest Std. Dev. 5.785503
75% 25 34
90% 29 35 Variance 33.47205
95% 34 35 Skewness .9487176
99% 41 41 Kurtosis 3.975005
In the above output, the largest value in 75% is 34, while the starting value of
90% is 29. The same is with the 95%. Why this is so? Shouldn't the percentile
value be monotonically increasing? I am interested in this because in one of my
own data, I have obtained the following output:
uprice
-------------------------------------------------------------
Percentiles Smallest
1% .0022779 .0001697
5% .01875 .0002087
10% .0581161 .0010804 Obs 626
25% .3826962 .0012382 Sum of Wgt. 626
50% 1.667209 Mean 79.44026
Largest Std. Dev. 432.1083
75% 9.730152 2658.562
90% 77.09222 3077.629 Variance 186717.6
95% 363.5599 5423.877 Skewness 11.04796
99% 1490.65 7004.734 Kurtosis 151.0011
where as you can see I have a similar problem (largest value in 75% is much
higher than the starting value in 90% and so on). I am guessing that this is due
to the 3rd (skewness) and 4th (kurtosis) moments of the distribution. But I do
not have a convincing interpretation/explanation. Your help will be much
appreciated.
Regards,
Syed Basher
Qatar National Food Security Programme
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