RESUMO
INTRODUCTION: The Multidimensional Weight Locus of Control Scale (MWLCS) measures a person's beliefs regarding the locus of control or lack of locus of control over his/her body weight. PURPOSE: We aim to evaluate the factorial structure and psychometric properties of the MWLCS with Spanish normal weight, overweight and obese samples. METHODS: The research was carried out in two different studies. The first included a sample of 140 normal weight participants, selected out of a 274 sample recruited with an online survey. Study 2 was carried out in a sample of 633 participants recruited from the PREDIMED-Plus study. Out of them, 558 participants fulfilled the weight criteria and were categorized into: overweight (BMI 25 - < 29.99; N = 170), obese class I (BMI 30 - < 34.99; N = 266), and obese class II (BMI 35 - < 39.99; N = 122). Exploratory (EFA) and confirmatory (CFA) factor analyses were used to evaluate the factor structure of the MWLCS, and reliabilities and Spearman's correlations were estimated. Invariance measurement was tested across the three subgroups of weight in Study 2. RESULTS: A three-factor structure indicating weight locus of control factors (internal, chance, and powerful others) was supported, both via EFA in the normal weight sample and CFA in the overweight and obese samples. In the normal weight sample, the powerful others dimension was positively related to BMI and the dimensions of the Dutch Eating Behaviors Questionnaire. Additionally, the scale showed evidence of scalar invariance across the groups with different weight conditions. CONCLUSIONS: This scale seems to be a psychometrically appropriate instrument and its use is highly recommended when designing interventions for overweight or obese individuals. LEVEL OF EVIDENCE: Level V, descriptive study.