Lay versus expert interviewers for the diagnosis of migraine in a large sample of elderly people.

OBJECTIVE To determine the agreement between lay interviewers and experts in the diagnosis of migraine by questionnaire. SUBJECTS A population based sample of 1188 individuals aged 64 to 73 years. METHODS Participants who declared that they had recurrent headaches (n = 238) answered a structured questionnaire by lay interviewers with special training in migraine. A migraine expert subsequently interviewed all the headache sufferers using the same questionnaire. Migraine was defined according to the International Headache Society criteria. RESULTS In comparison with the expert, the diagnosis derived by the lay interviewers had high values for specificity (97%) and positive predictive value (86%), and a low sensitivity (50%) and negative predictive value (57%). Agreement between the expert and the lay interviewers was low, with a kappa value of 0.36 (95% confidence interval 0.26 to 0.47). The most serious discrepancies concerned the duration of attacks, the worsening of headaches by physical activity, the presence of nausea or vomiting, and the unilaterality of headaches. As a result, the lifetime prevalence of migraine headaches was greatly underestimated by lay interviewers (6.5%) in comparison with the expert (11.1%). CONCLUSIONS A low level of agreement between lay interviewers and a headache expert in the diagnosis of migraine headaches by structured questionnaire may result in a substantial underestimation of migraine prevalence.