  In the most popular approach to the numerical study of the Anderson
metal-insulator transition the transfer matrix method is combined with
finite-size scaling ideas. This approach requires large computer resources to
overcome the statistical fluctuations and to accumulate data for a sufficient
range of different values of disorder or energy. In this paper we present an
alternative approach in which the basic transfer matrix is extended to
calculate the derivative with respect to disorder. By so doing we are able to
concentrate on a single value of energy or disorder and, potentially, to
calculate the critical behaviour much more efficiently and independently of the
assumed range of the critical regime. We present some initial results which
illustrate both the advantages and the drawbacks of the method.
