title: Modelling neuromotor ratings with floor-effects.
abstract: Associated movements (AMs) are a classical diagnostic tool to assess differences between normal children and children with some motor dysfunction. This paper presents a methodology to produce age- and gender-dependent reference-curves for AMs of normal children, for various tasks of a test battery. Data available consist of separate ratings of duration and extent of AMs, which are ordinal quantities with few levels. Other problems are severe age- and gender-dependent floor-effects (as well as some ceiling-effects), leaving little information for analysis at older ages. To get a better scale, we combined the two ordinal ratings into one meaningful and quasi-continuous quantity referred to as intensity of AMs. In order to solve problems due to floor-effects, ceiling-effects and discreteness, we assumed left- , right- and interval-censored values, respectively. We considered a censored regression problem and postulated a truncated normal distribution for the non-censored values (after an appropriate transformation of the data). Using Wei and Tanner's poor man's data augmentation algorithm, together with the technique of linear mixed effects modelling, useful reference-curves could be produced. In contrast to the cumulative probabilities approach for ordinal data, our methodology allows the calculation of individual age- and gender-standardized values, which puts us in a position to investigate numerous scientific questions.
authors.affiliation: Department of Biostatistics, Institute for Social and Preventive Medicine, University of Zürich, Sumatrastrasse 30, CH-8006 Zürich, Switzerland.
authors.forename: Theo
authors.initials: T
authors.lastname: Gasser
authors.forename: Valentin
authors.initials: V
authors.lastname: Rousson
mesh_terms: D000293:Adolescent; D000465:Algorithms; D001699:Biometry; D002648:Child; D005260:Female; D006801:Humans; D016014:Linear Models; D008297:Male; D008959:Models, Neurological; D015233:Models, Statistical; D016472:Motor Neuron Disease / Q000175:diagnosis* / Q000503:physiopathology; D009048:Motor Skills; D009068:Movement; D012016:Reference Values