title: [Roaming through the methodology. XXVIII. More problems with longitudinal studies: dropouts, head-start effects and interval correlations].
abstract: The Amsterdam Growth and Health Longitudinal Study with about 300 teenage boys and girls illustrates a number of problems that can occur in a longitudinal study. By adopting a more complex study design (multiple birth cohorts and a separate control group without longitudinal measurements) confounding factors may be found. A problem with the longitudinal design are the dropouts: by comparing their study results in the period before the dropout with the results of the 'stayers' in the same period, selective dropout may be identified. In a multiple longitudinal design with overlapping cohorts, head-tail effects may occur: the most reliable results are found in the middle area where there is the most overlap. Interperiod correlations may assist in determining the stability and the accuracy of the measurements.
authors.affiliation: Vrije Universiteit, Faculteit der Geneeskunde, Instituut voor Extramuraal Geneeskundig Onderzoek, Van der Boechorststraat 7, 1081 BT Amsterdam. hcg.kemper.emgo@med.vu.nl
authors.forename: H C
authors.initials: HC
authors.lastname: Kemper
mesh_terms: D000293:Adolescent; D015986:Confounding Factors, Epidemiologic; D003627:Data Interpretation, Statistical; D015340:Epidemiologic Research Design; D006801:Humans; D008137:Longitudinal Studies; D010352:Patient Dropouts / Q000706:statistics & numerical data; D016008:Statistical Distributions