The Introduction defines the problem under discussion and distinguishes between subjective, objective and semi-objective tests. The author then considers subjective telephone tests in greater detail, and emphasizes the importance of testing for “fitness for purpose” under conditions similar to those of practical use. There follows a discussion of the application of the results of subjective tests to practical cases, in the course of which the arguments are put forward for the statistical extension of the results of immediate-appreciation tests. An account is then given of the application of the statistical technique to immediate-appreciation tests, and the author concludes with some suggestions as to how the effects of speaking-end room-noise may be included in the statistical technique. A short bibliography is appended.