Introduction“I can't concentrate, doctor” is a common complaint among psychiatric patients. The phrase is usually applied in a general sense to describe a state in which the patient has ceased to read the newspapers or watch the television and can no longer cope adequately with his work. In clinical practice the performance of the “serial sevens” test has been thought to give an indication of impairment of this function, whatever it may be (Mayer-Gross, Slater and Roth, 1960). As the symptom is so common, a measure of its severity may be of some value. This paper describes an attempt to develop such a measure and discusses the possible implications of its failure.