A single question about prior stroke versus a stroke questionnaire to assess stroke prevalence in populations

Background: False-positive and false-negative answers to screening question s influence prevalence and incidence estimations for stroke in population s tudies. Despite frequent use in screening, only a few studies have examined causes and influence of incorrect self-reports. We compared the rates of f alse-positive and false-negative answers to a single question about prior s troke to those of the Stroke Symptom Questionnaire (SSQ), a newly developed instrument based on 6 symptom questions. Differences in stroke prevalence estimations and risk factors for incorrect reports are described. Methods: The MEMO study (Memory and Morbidity in Augsburg Elderly) examines cognitiv e function and neurodegenerative diseases in an elderly population (n = 384 ) in southern Germany. All participants filled in the symptom questionnaire , received a neurological examination and a neuropsychological test battery . Medical records were obtained for event validation of subjects positive o n screening and those negative on screening with symptoms suggesting a cere brovascular event during examination. Results: Prevalence of total stroke w as 5.3% using a single screening question and 6.8% using the questionnaire. The false-negative rate was higher for the single-question approach (34.2 versus 10.5%). It was strongly influenced by gender a nd cognitive function . The questionnaire had a higher false-positive rate than the single questi on. Based on the results, we established question combinations that best se rved three different research scenarios (frequency estimation, risk factor analysis, control selection), relevant to stroke research in population stu dies. Conclusions: A single screening question for stroke in the past with event validation by medical records underestimates stroke frequency in popu lation studies by about 30%. Use of a number of questions for key symptoms combined with a general stroke question, as in the SSQ, improves the comple teness of event ascertainment and allows the detection of stroke and transi ent ischemic attack at the same time. Copyright (C) 2000 S. Karger AG, Base l.