Corbett et al (1987) reported recently that porosity, smectite content, and percent strain at failure were significant parameters controlling the Austin Chalk’s strength. They based this conclusion on results of multiple linear regression analyses of data from rock-failure experiments. There are, however, inconsistencies between their regression analyses and experimental procedure. In this discussion, I correct the multiple regression analyses of Corbett et al (1987) and demonstrate that confining pressure is a more appropriate predictor of rock strength than strain at failure. Finally, I emphasize that multiple linear regression is best used after an investigator first has made explicit a causal...

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