Psychometric evaluation of the muscle dysmorphic disorder inventory (MDDI) among gender-expansive people

Purpose: Muscle dysmorphia is generally classified as a specific form of body dysmorphic disorder characterized by a pathological drive for muscularity and the preoccupation that one is too small or not sufficiently muscular. The majority of research on the condition has been conducted in cisgender men with a paucity of literature on gender minority people, a population that is at risk for muscle dysmorphia. One of the most widely used measures of muscle dysmorphia symptoms, the Muscle Dysmorphic Disorder Inventory (MDDI), has not been psychometrically validated for use in gender minority samples, the aim of the present study. Methods: We evaluated the psychometric properties of the MDDI in a sample of 1031 gender-expansive individuals (gender minority people whose gender identity differs from that assumed for their sex assigned at birth and is not exclusively binary man or woman) aged 18–74 who were part of The PRIDE Study, a large-scale, U.S., longitudinal cohort study. Results: Using a two-step, split-sample exploratory and confirmatory factor analytic approach, we found support for the original three-factor structure of the measure. The subscales showed adequate internal consistency, and convergent validity was supported based on significant associations of the MDDI subscale scores with theoretically related scores on a widely used measure of disordered eating. Conclusions: These findings provided novel support for adequate psychometric properties of the MDDI in a sample of gender-expansive individuals, facilitating the use of this measure in future research on muscle dysmorphia in this understudied and at-risk population.