[ncl-talk] stat_dispersion and standard deviation

[Rainer Luptowitz]

Hi ncl-talk,

Is the standard deviation computed in the "stats_dispersion" function
actually a variance?

I test this and it appears to be variance instead of stats_dispersion as
seen in with sample "a" below.


Variable: a
Type: float
Total Size: 56 bytes
            14 values
Number of Dimensions: 1
Dimensions and sizes: [ncl_join | 14]    ; I had joined 8 files trends with
"addfiles" function
Coordinates:
Number Of Attributes: 0
(0) -20.46505
(1) -4.795454
(2) -1.454606
(3) -2.677286
(4) -1.868608
(5) -0.4972475
(6) 1.18715
(7) -1.657706
(8) -3.428875
(9) -2.766053
(10) -1.689298
(11) -0.3371645
(12) -0.640966
(13) -0.7326741

; ncl code compare variance to standard deviation

; the above data was placed into an array named "a"
a = (/-20.46505, -4.795454, -1.454606,-2.677286, -1.868608, -0.4972475,
1.18715, -1.657706, -3.428875, -2.766053, -1.689298, -0.3371645, -0.640966,
-0.7326741/)


; Input
Var_a = variance(a)  ; calc variance
print(Var_a)
StdDev_a = stddev(a) ; calc standard deviation
print(StdDev_a)
opt = True
opt at PrintStat = True
Stats_a = stat_dispersion(a,opt)


; Output
; from individually calculating Variance
Variable: Var_a
Type: float
Total Size: 4 bytes
            1 values
Number of Dimensions: 1
Dimensions and sizes: [1]
Coordinates:
(0) 27.49021

; from individually calculating Standard Deviation
Variable: StdDev_a
Type: float
Total Size: 4 bytes
            1 values
Number of Dimensions: 1
Dimensions and sizes: [1]
Coordinates:
(0) 5.243111

; from Stats_Dispersion function.
(0)
(0)   ===> Robust Dispersion Statistics <===
(0) [0]            Mean=-2.98742
(0) [1]          StdDev=27.4902    ; this appears to be variance since
(0) [2]             Min=-20.4651
(0) [3]          LowDec=-20.4651
(0) [4]          LowOct=-20.4651
(0) [5]          LowSex=-4.79545
(0) [6]     LowQuartile=-3.42888
(0) [7]          LowTri=-2.76605
(0) [8]          Median=-1.6735
(0) [9]         HighTri=-1.45461
(0) [10]   HighQuartile=-0.732674
(0) [11]        HighSex=-0.640966
(0) [12]        HighOct=-0.497248
(0) [13]        HighDec=-0.497248
(0) [14]            Max=1.18715
(0) [15]          Range=21.6522
(0) [16]     Dispersion=0.787633
(0) [17]    RMS Anomaly=5.05239
(0) [18]      #   Total=14
(0) [19]      #    Used=14
(0) [20]      # Missing=0
(0) [21]      % Missing=0
(0) [22]     Lower 0.1%=9.96921e+36
(0) [23]     Lower 1.0%=9.96921e+36
(0) [24]     Lower 5.0%=9.96921e+36
(0) [25]     Upper 5.0%=9.96921e+36
(0) [26]     Upper 1.0%=9.96921e+36
(0) [27]     Upper 0.1%=9.96921e+36
(0) [28]       Skewness=-2.57898
(0) [29]       Kurtosis=5.86411


What do you think?

Thank you for time and assistance,

*Rainer Luptowitz*
*Grad Student *
*Dept Earth Sciences*
*UC Riverside*
*rlupt001 at ucr.edu* <rlupt001 at ucr.edu>
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