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Trend Analysis : Deseason?

eddie

January 09, 2013 13:42

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Hi Guys,

Just wondering if anybody could help me to understand why we shoud deseason the time series data before applying Trend Analysis in Earth Trend Modeller. Anybody?

Thanks in advance.

Cheers

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2 comments

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  Clark Labs Tech Support Team January 10, 2013 20:01

  Hi Eddie,

  Deseason removes the dramatic trends that accompany changing seasons. After removing seasonal trends many less apparent trends are more easily observed. You can read more about this important tool in the IDRISI Tutorial document (chapter 7, exercise 2).

  Best,
  
  Andrew Hostetler

  IDRISI Technical Support Team

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  eddie January 11, 2013 09:03

  Thank you very much Andrew. If I may share additional comments by Prof. Eastman here for the benefit of others.

  "For a non-parametric technique such as the Theil-Sen trend operator or the monotonic tend, it makes no difference. However, for the correlation measure, it makes an enormous difference because we remove a huge source of variance (the seasons). The OLS slope measure should be about the same, but the significance would be affected for the same reason. In general, deseasoning is advised."