The role and importance of measurement in scientific psychiatry is difficult to over-stress. It is a field where there is a fruitful interplay between the ideas typical of the 'medical model' of disease and those coming from the psychometric traditions of, say, educationalists or personality theorists. The style of this important text is problem-based rather then technique-led, thus encouraging thought in the use of statistical techniques, rather than a heavy reliance on formulae.