[Psychometric properties of the Eating Disorders Inventory among Portuguese adolescents].

Introduction: Although Eating Disorders Inventory (EDI) was developed with adults, a large amount of research about eating disorders in adolescents is usually conducted with EDI. The clinical and research utility of this instrument would be improved by analysing its psychometric properties when used with younger people than those in the original standardization samples. The main objective of our study is to analyse the psychometric properties of the Eating Disorders Inventory (EDI) among 13 year old Portuguese adolescents.

Methods: A sample of 1184 adolescents (641 girls and 543 boys) born in 1990 and attending public and private schools in Porto completed EDI and was evaluated with Stunkard Figure Scale at school. Anthropometric measurements were also performed. Internal consistency was analysed trough item-total correlations and Cronbach's alpha coefficients. Mann-Whitney and Kruskal-Wallis tests were used to evaluate construct validity.

Results: After the exclusion of 17 of the 64 items that showed low consistency, a correlation matrix of seven principal components, that explained 49.8% of the total variance, was obtained. In this matrix, 8 subscales with alpha ranging from 0.53 to 0.87 were defined. The three core EDI subscales (Drive for Thinness, Bulimia and Body Dissatisfaction) presented good psychometric properties and, except item 1 (item-total correlation= 0.00), items showed good internal consistency (item-total correlations ranging from 0.41 and 0.73, Cronbach's alpha ranging from 0.77 and 0.87). In accordance with theoretical constructs previously defined, girls presented higher mean scores than boys on Drive for Thinness subscale (4.0 vs. 1.7, p < 0.001). Also, adolescents with a healthy weight presented significantly lower scores than overweight adolescents in the same subscale. Boys and girls classified as dissatisfied or very dissatisfied with body image according to Stunkard Figure Rating Scale presented significantly higher scores on Body Dissatisfaction EDI subscale.

Conclusion: The Portuguese version of EDI, with the proposed changes, showed good psychometric characteristics to evaluate symptoms associated with eating disorders among 13 year old adolescents. The subscales Drive for Thinness, Bulimia and Body Dissatisfaction, besides presenting good psychometric properties, remained similar to the same subscales in the original EDI. The instrument is able to distinguish groups according to theoretical constructs.