title: Methodological issues in studying rates and predictors of migraine progression and remission.
abstract: BACKGROUND
  The progression and remission of migraine and the risk factors that determine the course of illness have been intensively studied for the past decade.
  
  
  METHODS
  In this fourth paper in a series of methodological articles, we summarize crucial issues that influence studies of migraine clinical course, and suggest directions and opportunities for future research.
  
  
  RESULTS
  Defining chronic migraine (CM) based on 15 or more headache days per month is problematic because headache frequency varies from month to month. We propose methods of defining CM as a trait and not as a state of headache frequency. Our notions of progression and remission, defined by the crossing of an arbitrary frequency boundary, are also problematic; we propose alternative approaches. Measuring headache frequency is challenging because of measurement error, temporal sampling error, and real change over time.
  
  
  CONCLUSIONS
  We suggest alternative approaches for defining migraine subtypes, measuring change in frequency, defining progression and remission, and modeling change over time. Our suggestions are intended to encourage dialogue and need refinement and evaluation. Our long-term goal is to improve classification and measurement to facilitate the discovery of risk factors, genes, and other biological processes that determine the onset and course of migraine.
authors.affiliation: Department of Neurology and the Montefiore Headache Center, Albert Einstein College of Medicine, Bronx, NY 10461, USA. richard.lipton@einstein.yu.edu
authors.forename: Richard B
authors.initials: RB
authors.lastname: Lipton
authors.forename: Donald B
authors.initials: DB
authors.lastname: Penzien
authors.forename: Dana P
authors.initials: DP
authors.lastname: Turner
authors.forename: Todd A
authors.initials: TA
authors.lastname: Smitherman
authors.forename: Timothy T
authors.initials: TT
authors.lastname: Houle
mesh_terms: D018450:Disease Progression; D006801:Humans; D008881:Migraine Disorders / Q000175:diagnosis* / Q000628:therapy*; D011237:Predictive Value of Tests; D012074:Remission Induction / Q000379:methods*; D012307:Risk Factors; D012720:Severity of Illness Index