This paper exhibits contemporary psychometric models of questionnaires with dichotomous items. Such as approach allows assessment of individual items in terms of precision of measurement in ways not previously available. This Latent Trait Model approach is used to analyse the responses of 3806 subjects to the Eysenck Personality Questionnaire (EPQ). Short forms, of 10 items length, are recommended; they are the best possible such short forms, in that they provide the most accurate possible measurement overall.