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I have several measurements of trees over time (different vegetation indexes).

Each measurement is in a different scale, some also include negative values (e.g. NDVI).

I need to compare the variation in time of all measurements, using a single statistical measure. Coefficient of variation is not relevant because of negative values. Can anyone recommend an approach?

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  • $\begingroup$ difficult. Can you give us more information about the different measures? $\endgroup$ – Ben Bolker Dec 21 '16 at 16:20
  • $\begingroup$ Thanks. the variables are based on various band(color) relations of images. See en.wikipedia.org/wiki/Vegetation_Index. The scale of the different variables differs; 0 to 1, -1 to 1 (as in NDVI), X to -X. Can skew help? maybe STD/range? $\endgroup$ – Gilad Weil Dec 21 '16 at 16:52
  • $\begingroup$ Even though I don't know why you were thinking of coefficient of variation negative values does not exclude as |mean| can be used in the denominator. The problem comes about when mean=0. $\endgroup$ – Michael Chernick Dec 21 '16 at 23:56
  • $\begingroup$ @MichaelChernick is absolute value of mean commonly used for coefficient of variation? I haven't seen that elsewhere and was curious if it's acceptable since I have a similar problem to the OP $\endgroup$ – qdread Jun 7 '18 at 16:05

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