Reliability in headache diagnosis.

The reliability of headache diagnosis using the criteria of the International Headache Society (IHS) has not been well studied. One definition of reliability refers to the reproducibility of diagnoses assigned to the same individual at different times. Reproducibility of diagnosis should be assessed using different clinicians at different times, with or without specific diagnostic instruments. A diagnosis may be unreliable because of variability in diagnostic criteria, in the clinical information used to assign diagnoses, or in the interpretation and application of clinical information to a given set of diagnostic criteria. Reliable diagnostic methods are essential to the development of valid diagnostic methods, as well as for the identification of headache risk factors, biological markers, and effective treatments. An approach to studying the reliability of the International Headache Society criteria is outlined, modeled after the extensive studies conducted in the area of psychiatric diagnosis.