title: Correct identification and explanation of age-related changes are always possible.
abstract: In this commentary, it is argued that the definition of the time or the age variable in the models presented by Hofer and Sliwinski is ambiguous, and a standard interpretation of this time of age variable is proposed instead. Some simulation studies are presented, the results of which indicate that, even with age-heterogeneous cross-sectional data, correct identification of the true sources of age-dependent variation is possible. An important qualification, based on new methodological work in progress, is given of the scope of longitudinal designs. It is concluded that all kinds of age-related changes are potentially interesting and can be correctly identified and explained.
authors.affiliation: University of Amsterdam, Roetersstraat 15, Room 502, NL-1018 WB Amsterdam, The Netherlands. op_molenaar@macmail.psy.uva.nl
authors.forename: Peter C M
authors.initials: PC
authors.lastname: Molenaar
mesh_terms: D000368:Aged; D000375:Aging / Q000502:physiology*; D006801:Humans; D008137:Longitudinal Studies; D015233:Models, Statistical