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Summary For the standard linear model containing several explanatory variables, the precision of estimation of linear parametric functions is analysed in terms of latent roots and vectors of X'X, where X is the matrix of values of explanatory variables. This analysis provides a practical method for detecting multicollinearity, and it is demonstrated that it is also useful in solving problems of optimum choice of new values of explanatory variables.
S. D. Silvey (Mon,) studied this question.