Juan Pablo Zapata-Ospina ^1* Natalia Rodríguez ² Ayda Margarita Rodríguez ² Jenny García-Valencia ² Mercedes Jiménez-Benítez ³ Nicolás Martínez ⁴ Diana Restrepo Bernal ⁵ Ana Lucía Gallego ⁶ Carolina Gómez ⁷ Luis Fernando Tabares ⁷ Carlos Cardeño-Castro ⁸ Daniel Camilo Aguirre-Acevedo ¹

• ¹ Institute of Medical Research, Facultad de Medicina, Universidad de Antioquia, Medellin, Antioquia, Colombia
• ² Departamento de Psiquiatría, Facultad de Medicina, Universidad de Antioquia, Medellin, Colombia
• ³ Department of Psychology, Faculty of Social and Human Sciences, University of Antioquia., Medellin, Colombia
• ⁴ Centro Javeriano de Oncología, San Ignacio University Hospital, Bogotá, Cundinamarca, Colombia
• ⁵ Faculty of Medicine, CES University, Medellín, Antioquia, Colombia
• ⁶ Universidad del Norte, Colombia, Barranquilla, Colombia
• ⁷ Hospital Alma Mater de Antioquia, Medellin, Colombia
• ⁸ Department of Psychiatry, Hospital Universitario de San Vicente Fundación, Medellín, Antioquia, Colombia

Background: Adjustment disorder (AD) is common among medically ill patients, yet current evaluation methods do not address the specific characteristics in this population. This study aimed to develop a measurement scale for AD in medically ill patients in Colombia and to find evidence of its validity and reliability.Methods: This was a scale development and validation study. In the first qualitative phase, items were developed. In the second phase, the content validity of each item was evaluated by patients and clinicians. In the third phase, structural validity, internal consistency, test-retest reliability, criterion validity, and convergent construct validity were assessed. Items were analyzed using a generalized partial credit model within an item response theory framework.Results: The Adjustment Disorder Scale for Medically Ill Patients (ETAM, for its acronym in Spanish) was developed, comprising 20 items that address the free description of stressful situations in the last 15 days and mental symptoms attributed to them. Evidence of content validity was found. The scale was administered to 512 medically ill patients, revealing a three-dimensional structure: 1) "AD Symptoms," 2) "Impact on Self-Care," and 3) "Impact on Desire to Live." Internal consistency was adequate, with McDonald's omega of 0.95 and Cronbach's alpha between 0.82 and 0.92 for its dimensions. ETAM had high test-retest reliability (intraclass correlation coefficient of 0.98). Criterion validity evidence was obtained with an independent psychiatrist's diagnosis, with an AUROC of 0.99, and convergent validity was consistent with hypotheses of correlation with other instruments with similar constructs. Discrimination and difficulty parameters were calculated for each item.The ETAM is a scale with evidence of validity and reliability that can be used for the diagnosis of AD in medically ill patients in Colombia.