1. A diagnostic apparatus for use in relation to an industrial process, the apparatus comprising a data processing apparatus programmed to: receive object data for a set of product units that have been subjected nominally to the same industrial process, the object data for each product unit representing one or more parameters measured on the product unit at points spatially distributed across the product unit; define a multidimensional space in which the object data for each of the said product units can be represented as a vector; perform a multivariate analysis on the object data to obtain one or more component vectors in the multidimensional space; and extract diagnostic information about the industrial process using the component vectors.