title: Methods for analyzing observational longitudinal prognosis studies for rheumatic diseases: a review & worked example using a clinic-based cohort of juvenile dermatomyositis patients.
abstract: Most outcome studies of rheumatic diseases report outcomes ascertained on a single occasion. While single assessments are sufficient for terminal or irreversible outcomes, they may not be sufficiently informative if outcomes change or fluctuate over time. Consequently, longitudinal studies that measure non-terminal outcomes repeatedly afford a better understanding of disease evolution.Longitudinal studies require special analytic methods. Newer longitudinal analytic methods have evolved tremendously to deal with common challenges in longitudinal observational studies. In recent years, an increasing number of studies have used longitudinal design. This review aims to help readers understand and apply the findings from longitudinal studies. Using a cohort of children with juvenile dermatomyositis (JDM), we illustrate how to study evolution of disease activity in JDM using longitudinal methods.
authors.affiliation: Children's Hospital Research Institute of Manitoba, University of Manitoba, Winnipeg, Canada. llim@chrim.ca.|Department of Pediatrics, University of Manitoba, Winnipeg, Canada. llim@chrim.ca.|Institute of Health Policy Management and Evaluation, University of Toronto, Toronto, Canada. llim@chrim.ca.
authors.forename: Lily Siok Hoon
authors.initials: LS
authors.lastname: Lim
authors.affiliation: The Child Health Evaluative Sciences Program, SickKids Research Institute, Toronto, Canada.
authors.forename: Eleanor
authors.initials: E
authors.lastname: Pullenayegum
authors.affiliation: Department of Family and Community Medicine, University of Toronto, Toronto, Canada.
authors.forename: Rahim
authors.initials: R
authors.lastname: Moineddin
authors.affiliation: Department of Medicine, Toronto Western Research Institute, University of Toronto, Toronto, Canada.|Centre for Prognosis Studies, University Health Network, Toronto Western Hospital, Toronto, Canada.
authors.forename: Dafna D
authors.initials: DD
authors.lastname: Gladman
authors.affiliation: Division of Rheumatology, SickKids, Toronto, Canada.|Physiology and Experimental Medicine Program, SickKids Research Institute, Toronto, Canada.|Department of Pediatrics and Immunology, University of Toronto, Toronto, Canada.
authors.forename: Earl D
authors.initials: ED
authors.lastname: Silverman
authors.affiliation: Institute of Health Policy Management and Evaluation, University of Toronto, Toronto, Canada.|The Child Health Evaluative Sciences Program, SickKids Research Institute, Toronto, Canada.|Division of Rheumatology, SickKids, Toronto, Canada.|Department of Pediatrics and Immunology, University of Toronto, Toronto, Canada.|The Dalla Lana School of Public Health, University of Toronto, Toronto, Canada.
authors.forename: Brian M
authors.initials: BM
authors.lastname: Feldman
mesh_terms: D000704:Analysis of Variance; D056808:Biostatistics; D002648:Child; D003882:Dermatomyositis / Q000453:epidemiology*; D006801:Humans; D008137:Longitudinal Studies; D008954:Models, Biological; D064887:Observational Studies as Topic / Q000379:methods* / Q000706:statistics & numerical data; D011379:Prognosis; D012216:Rheumatic Diseases / Q000453:epidemiology*
keywords: Biostatistics; Childhood-onset dermatomyositis; Epidemiology; Longitudinal study