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Applied Statistics Using SPSS, STATISTICA, MATLAB and R

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390 10 Directional Data<br />

*<br />

2<br />

z = ( 1−1<br />

/( 2 n))<br />

z + z /( 10 n)<br />

, 10.19<br />

it can be proven that the distribution of z * is asymptotically<br />

2<br />

χ 3 with an error<br />

decreasing as 1/n (Mardia KV, Jupp PE, 2000).<br />

The Rayleigh test is implemented in <strong>MATLAB</strong> <strong>and</strong> R function rayleigh (see<br />

Comm<strong>and</strong>s 10.5)<br />

Example 10.11<br />

Q: Apply the Rayleigh test to the wind direction WDF data of the Weather<br />

dataset <strong>and</strong> to the measurement data M1 of the Soil Pollution dataset.<br />

A: Denoting by wdf <strong>and</strong> m1 the matrices for the datasets, the probability values<br />

under the null hypothesis are obtained in <strong>MATLAB</strong> as follows:<br />

» p=rayleigh(wdf)<br />

p =<br />

0.1906<br />

» p=rayleigh(m1)<br />

p =<br />

0<br />

Thus, we accept the null hypothesis of uniformity at the 5% level for the WDF<br />

data, <strong>and</strong> reject it for the soil pollution M1 data (see Figure 10.9).<br />

X<br />

Figure 10.9. Measurement set M1 (negative gradient of Pb-tetraethyl concentration<br />

in the soil) of the Soil Pollution dataset.<br />

Z<br />

Y

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