Medical care
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Reliability and validity are as necessary for predrafted advance directive forms as they are for all clinical assessment instruments. Performance of predrafted advance directive forms with both lay persons and clinicians is relevant. Evidence relating to test- retest reliability, content validity, and criterion-related validity of one form, the Medical Directive, has been documented for outpatients. The authors investigated construct validity and external validity among outpatients, physicians, and the general public. ⋯ The Medical Directive has construct validity in relations among specific treatment preferences and between treatment preferences, illness scenarios, and goals for care. External validity is supported by study of separate outpatient, physician, and general public populations. The treatment items constitute a highly reliable scale that can be used in further empirical research regarding life-sustaining treatment.