Unfortunately as Mark has noted, if nothing is known then one will have to design a sampling plan using other criteriia, i.e., essentially meaning non-statistical criteria. Even if there were no spatial correlation and one only wanted to estimate the average value for the block one would need the variance. In such a case one might iterate, i.e., randomly select sample locations (the number being determined perhaps by budget and difficulty of sampling). After sampling at those locations, compute the sample variance and use this to "predict" a sample size (which will almost certainly be larger than the original size). One can of course use the data obtained at this stage to estimate the mean and also obtain a confidence interval, the new sample size will be related to the desired confidence interval width and desired confidence level. Having determined a "new" sample size, repeat the process (combining the original sample with the new data would not correspond to random sampling), if after several iterations it appears that the predicted sample size stablizes then you are through. Note that this process only focuses on the "number" of sample locations, the actual locations being selected randomly. This process can be improved on by using the theory of sequential sampling. With respect to geostatistics, we need to remember that the data (in common practice) is used for two different purposes.The first being the estimation/modeling of the variogram or covariance function, the second being the kriging (of whatever form or type). An optimal sampling plan for the one will generally not be an optimal plan for the other. There is an old issue of "GEOSTATISTICS", the NACOG newsletter, that has a long list of papers on sampling design. A number of papers have been written since then as well. There is no definitive answer to the question since it depends on the question, i.e., what is the data to be used for? Donald E. Myers Department of Mathematics University of Arizona Tucson, AZ 85721 http://www.u.arizona.edu/~donaldm -- * 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
