Factor structure and psychometric properties of the Muscle Dysmorphic Disorder Inventory (MDDI) among transgender women

Muscle dysmorphia (MD) is characterized by extreme preoccupation with insufficient muscularity that prompts pathological behaviors and distress/impairment. The Muscle Dysmorphic Disorder Inventory (MDDI) - a widely used measure of MD symptoms - has yet to be validated among transgender women, despite emerging evidence suggesting risk for muscularity-oriented concerns in this population. We examined the MDDI factor structure as well as the reliability and validity of its subscales in a sample of 181 transgender women ages 19-73 years who participated in a national longitudinal cohort study of U.S. sexual and gender minority adults. Confirmatory factor analysis was used to examine model fit for the original three-factor structure of the MDDI (drive for size, appearance intolerance, functional impairment). A re-specified three-factor model allowing covariance of residuals for two conceptually related items demonstrated good overall fit (χ²/df = 1.33, CFI =.94, TLI =.93, RMSEA =.06 [95 % CI =.01,.09], SRMR =.07). Moreover, results supported the internal consistency and convergent and discriminant validity of the MDDI subscales in transgender women. Findings inform the use of the MDDI among transgender women and provide a foundation to support future research on the MDDI and MD symptoms among gender minority populations.