Hi, I have to recognize that i am very interested in this topic.
I did QQ norm plots on my data, and it is curved - but it is not an ... arc ... or how can i explain it? the lower part of the graph is almost a line for about 2/3 or the data and after it is a curve - kind of large - and after the rest of the data is almost on another line. Because the curvature is large it is hard to decide where to "split" the data with the naked eye. So i used box-plot to identify "outliers" and see if a QQ norm plot of these points represents a line or not. Well, it is not a perfect line - but it is quite close. So i was happy with that. But i plot in a QQ graph the rest of the "non-outliers" - and guess what??? It is a kind of curve, the nice line i had before in the first graph is now "diluted" (if i can say that) .... I know from the data semi-variogram that i don't have spatial autocorrelation - and i should. If i eliminate the "outliers" i do have spatial autocorrelation, with a decent global Moran's I. Now, if i reintroduce some of the previous identified "outliers", the global Moran's I increases. I would interpret this saying that box-plot over- estimated in this case the number of outliers. I have prior knowledge about the site i am working on, and since the contamination i am speaking about is PAH16, even so called background contamination (which is way below the environmental threshold) is anthropogenic in origin. Of course i am much more interested in "outliers" because there i have the "pollution" values. These values mainly cluster in 3 areas, and i consider those the "point source pollution" which actually correlate well with the industrial activity on the site. I think this is a nice and quite believable story. But the situation is totally different with heavy metals, or better put - not so obvious. So i am trying now to apply some MIX procedures (P. Mcdonald) and see if this will shed more light. Now my fear is that the spatial autocorrelation for heavy metals is at a much smaller scale than the actual sampling i have for the site.Unfortunately it is out of question to do more sampling. Monica -- * To post a message to the list, send it to [EMAIL PROTECTED] * As a general service to the users, please remember to post a summary of any useful responses to your questions. * To unsubscribe, send an email to [EMAIL PROTECTED] with no subject and "unsubscribe ai-geostats" followed by "end" on the next line in the message body. DO NOT SEND Subscribe/Unsubscribe requests to the list * Support to the list is provided at http://www.ai-geostats.org
