Too few samples and/or parameter difficult to predict and/or noise in the reference method are possible causes of large difference between SEC and SECV

From NIR Forum discussion Posted on Tuesday, February 08, 2011 - 4:42 am:    Dear all,  First, I want to say thank you in advance for every answer. I'm first time on this forum.  I have read a lot of things here and I  think that it is really useful. I have a question regarding the prediction of wood properties with NIR spectra.  I have a set of spectra from wood sample (calibration and test set) and I would like develop the best model for wood properties (eg wood density). However, I get higher error for cross validation (SECV) then for calibration set (SEC) and test set(SEP).Maybe I make a mistake in the application of cross validation. I use Unscrambler software. Can anyone tell me how to use the option of cross validation in Unscrambler software?  Thank you and best regards,  Nebojsa

Posted on Tuesday, February 08, 2011 - 5:44 am:    HI,  How large is the difference between SEC and SECV?  Before calibrating, you have to know the SEL (error of the reference method) and the SD of the calibration sample.  How many samples?  the gap between SEC and SECV is due to  - Too few samples and/or  - Parameter difficult to predict and/or  - Noise in the reference method.  SECV is always higher than SEC. My rule is to have SECV<=1.05*SEC with 2 groups of CV. Then I am pretty sure the model is robust.  Pierre

Posted on Tuesday, February 08, 2011 - 7:22 am: