Teresa Rivas

Application of the Double Monotonicity Model to Polytomous Items

Abstract. This paper investigates the item scalability of the Beck Depression Inventory (BDI) in 252 subjects; 126 with and 126 without eating disorders. To do so, an order was established regarding the BDI items according to the clinical characteristics of the subjects with eating disorders. The nonparametric Item Response Theory (NIRT) model was applied to evaluate Monotone Homogeneity and Double Monotonicity of items, as well as the reliability of the scale in both groups. The results show that the order of the items is satisfied in the group with eating disorders, but not in the control group. Therefore, the results obtained allow the ordering of depression scores of subjects with eating disorders according to their clinical characteristics. This order is not valid for the depression scores of subjects who did not have eating disorders. It should be noted that the application of the Double Monotonicity model to polytomous items provides new and relevant information when compared to the data provided b...

Factor Analysis of the Spanish Version of the Weight Efficacy Life-Style Questionnaire

This study examined the factor structure and psychometric properties of the Spanish version of the Weight Efficacy Life-Style Questionnaire (WEL), an instrument developed to measure self-efficacy in relation to food intake. A total of 292 Spanish persons participated, from three groups: clinical group, overweight group, and normal-weight group. The findings showed evidence of three situational factors (Negative Emotions, Social Pressure, and Physical Discomfort). The confirmatory factor analysis corroborated the three-factor model on an independent sample (N = 345). The results show a high degree of internal consistency of the scores of WEL. Significant correlations were found between the WEL scores and other variables that were hypothesized would be related to them. Significant differences on self-efficacy scores were found between some of the groups. The scores of WEL also significantly correlated with the Eating Self-Efficacy Scale scores. Finally, results are discussed and future research directions are suggested.

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

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.