These data record the percentage of coal ash found in mining samples originally reported by Gomez and Hazen (1970) and subsequently used by Cressie (1993).
The variables are:
||a code for east-west direction|
||a code for north-south direction|
||the percentage of coalash|
Cressie, N. (1993). Statistics for Spatial Data, revised edition. New York: Wiley.
Gomez, M. and Hazen, K. (1970). Evaluating sulfur and ash distribution in coal seams by statistical response surface regression analysis. Report RI 7377, U.S. Bureau of Mines, Washington, D. C.
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