title: The Non-uniqueness Property of the Intrinsic Estimator in APC Models.
abstract: This article explores an important property of the intrinsic estimator that has received no attention in literature: the age, period, and cohort estimates of the intrinsic estimator are not unique but vary with the parameterization and reference categories chosen for these variables. We give a formal proof of the non-uniqueness property for effect coding and dummy variable coding. Using data on female mortality in the United States over the years 1960-1999, we show that the variation in the results obtained for different parameterizations and reference categories is substantial and leads to contradictory conclusions. We conclude that the non-uniqueness property is a new argument for not routinely applying the intrinsic estimator.
authors.affiliation: Sociology and Social Sciences Research Methods, Radboud University Nijmegen, P.O. Box 9104, 6500 HC, Nijmegen, The Netherlands, b.pelzer@maw.ru.nl.
authors.forename: Ben
authors.initials: B
authors.lastname: Pelzer
authors.forename: Manfred
authors.initials: M
authors.lastname: te Grotenhuis
authors.forename: Rob
authors.initials: R
authors.lastname: Eisinga
authors.forename: Alexander W
authors.initials: AW
authors.lastname: Schmidt-Catran
mesh_terms: D000293:Adolescent; D000328:Adult; D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D002648:Child; D002675:Child, Preschool; D015331:Cohort Studies; D003627:Data Interpretation, Statistical; D005260:Female; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D008875:Middle Aged; D009026:Mortality; D013997:Time Factors; D014481:United States; D055815:Young Adult