coalash {sm}

Coal ash in mining samples

Description

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:

East	a code for east-west direction
North	a code for north-south direction
Percent	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.