Gregoire-
Sounds like white noise to me and your estimate is the mean eg 3 point example Input -1 0 1 Est 0 0 0 Res 1 0 -1 (as est-input) Is your variogram high nugget? Robert (Bob) L. Sandefur PE Senior Geostatistician / Reserve Analyst CAM 200 Union Suite 430 Lakewood, Co 80228 From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Gregoire Dubois Sent: Wednesday, January 30, 2008 05:00 To: ai-geostats@jrc.it Subject: AI-GEOSTATS: Correlation between kriging residuals and input data Dear list, Having fit a variogram to a dataset (indoor radon measurements) and applied cross-validations, I noticed the perfect negative correlation (-0.95) between my kriging residuals and my input data. This means that I am overestimating as much the low values as I am underestimating the high values, something I am expecting since the mean of the residuals -> 0, a property of kriging. Fine so far. What I am puzzled about is of the possible reasons of getting such a strong slope (close to -1) of the plot of my residuals against my input data? This, I understand, highlights that I am doing a systematic error somewhere which I want to avoid obviously. I thought I extracted properly the spatially correlated component of my dataset (the variogram of my residuals seems to show a pure nugget effect) but I still can't find any reasonable explanation for the systematic errors. Any hints? I must have missed something obvious here. Many thanks for any feedback. Best regards, Gregoire
