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A General Equation to Obtain Multiple Cut-off Scores on a Test from Multinomial Logistic Regression

Published online by Cambridge University Press:  10 January 2013

Rosa Bersabé*
Affiliation:
Universidad de Málaga (Spain)
Teresa Rivas
Affiliation:
Universidad de Málaga (Spain)
*
Correspondence concerning this article should be adressed to Rosa Bersabé Morán. Departamento de Psicobiología y Metodología de las Ciencias del Comportamiento. Facultad de Psicología. Universidad de Málaga. 29071 Málaga. (Spain). E-mail: bersabe@uma.es

Abstract

The authors derive a general equation to compute multiple cut-offs on a total test score in order to classify individuals into more than two ordinal categories. The equation is derived from the multinomial logistic regression (MLR) model, which is an extension of the binary logistic regression (BLR) model to accommodate polytomous outcome variables. From this analytical procedure, cut-off scores are established at the test score (the predictor variable) at which an individual is as likely to be in category j as in category j+1 of an ordinal outcome variable. The application of the complete procedure is illustrated by an example with data from an actual study on eating disorders. In this example, two cut-off scores on the Eating Attitudes Test (EAT-26) scores are obtained in order to classify individuals into three ordinal categories: asymptomatic, symptomatic and eating disorder. Diagnoses were made from the responses to a self-report (Q-EDD) that operationalises DSM-IV criteria for eating disorders. Alternatives to the MLR model to set multiple cut-off scores are discussed.

En este artículo, las autoras derivan una ecuación general para calcular múltiples puntos de corte en la puntuación total de un test con el fin de clasificar a los individuos en más de dos categorías ordinales. La ecuación se deriva a partir del modelo de regresión logística multinomial (RLM), que es una extensión del modelo de regresión logística binaria (BLR) para variables de respuesta politómica. Con este procedimiento analítico, los puntos de corte se establecen en la puntuación del test (la variable predictora) en la que un individuo tiene la misma probabilidad de pertenecer a la categoría j que a la categoría j+1 de una variable de respuesta ordinal. La aplicación del procedimiento completo se ilustra a través de un ejemplo con datos de un estudio real sobre trastornos de la conducta alimentaria. En este ejemplo se obtienen dos puntos de corte en las puntuaciones del Test de Actitudes Alimentarias (EAT-26) para clasificar a los individuos en tres categorías ordinales: asintomático, sintomático o con trastorno de la conducta alimentaria. Los diagnósticos se obtuvieron a partir de las respuestas a un autoinforme (Q-EDD) en el que se operativizan los criterios del DSM-IV para los trastornos de la conducta alimentaria. Se discuten diferentes alternativas al modelo RLM para establecer múltiples puntos de corte.

Type
Research Article
Copyright
Copyright © Cambridge University Press 2010

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