title: Use of inverse probability weighting to adjust for non-participation in estimating brain volumes in schizophrenia patients.
abstract: Low participation is a potential source of bias in population-based studies. This article presents use of inverse probability weighting (IPW) in adjusting for non-participation in estimation of brain volumes among subjects with schizophrenia. Altogether 101 schizophrenia subjects and 187 non-psychotic comparison subjects belonging to the Northern Finland 1966 Birth Cohort were invited to participate in a field study during 1999-2001. Volumes of grey matter (GM), white matter (WM) and cerebrospinal fluid (CSF) were compared between the 54 participating schizophrenia subjects and 100 comparison subjects. IPW by illness-related auxiliary variables did not affect the estimated GM and WM mean volumes, but increased the estimated CSF mean volume in schizophrenia subjects. When adjusted for intracranial volume and family history of psychosis, IPW led to smaller estimated GM and WM mean volumes. Especially IPW by a disability pension and a higher amount of hospitalisation due to psychosis had effect on estimated mean brain volumes. The IPW method can be used to improve estimates affected by non-participation by reflecting the true differences in the target population.
authors.affiliation: Department of Psychiatry, Institute of Clinical Medicine, University of Oulu, Oulu, Finland; Department of Diagnostic Radiology, Oulu University Hospital, Oulu, Finland; Department of Physiology, Institute of Biomedicine, and Biocenter Oulu, University of Oulu, Oulu, Finland. Electronic address: marianne.haapea@oulu.fi.
authors.forename: Marianne
authors.initials: M
authors.lastname: Haapea
authors.affiliation: Department of Psychiatry, Institute of Clinical Medicine, University of Oulu, Oulu, Finland; Department of Psychiatry, Oulu University Hospital, Oulu, Finland.
authors.forename: Juha
authors.initials: J
authors.lastname: Veijola
authors.affiliation: Department of Diagnostic Radiology, Oulu University Hospital, Oulu, Finland.
authors.forename: Päivikki
authors.initials: P
authors.lastname: Tanskanen
authors.affiliation: Department of Psychiatry, Institute of Clinical Medicine, University of Oulu, Oulu, Finland; Department of Psychiatry, Oulu University Hospital, Oulu, Finland.
authors.forename: Erika
authors.initials: E
authors.lastname: Jääskeläinen
authors.affiliation: Department of Psychiatry, Institute of Clinical Medicine, University of Oulu, Oulu, Finland; Department of Psychiatry, Oulu University Hospital, Oulu, Finland.
authors.forename: Matti
authors.initials: M
authors.lastname: Isohanni
authors.affiliation: Department of Psychiatry, Institute of Clinical Medicine, University of Oulu, Oulu, Finland; Department of Psychiatry, Oulu University Hospital, Oulu, Finland; Institute of Health Sciences, University of Oulu, Oulu, Finland.
authors.forename: Jouko
authors.initials: J
authors.lastname: Miettunen
mesh_terms: D017668:Age of Onset; D000704:Analysis of Variance; D001921:Brain / Q000473:pathology*; D015331:Cohort Studies; D004185:Disability Evaluation; D005260:Female; D005387:Finland; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008279:Magnetic Resonance Imaging; D008297:Male; D016017:Odds Ratio; D011336:Probability; D012044:Regression Analysis; D012189:Retrospective Studies; D012559:Schizophrenia / Q000134:cerebrospinal fluid / Q000473:pathology*