Objective: To develop a valid and reliable instrument for measuring attitudes toward osteopathic medicine.

Methods: Participants included 5,669 first-year students from 33 U.S. colleges of osteopathic medicine, who completed an online survey at the beginning of the 2019-2020 academic year. Using data from the nationwide Project in Osteopathic Medical Education and Empathy, we developed a 13-item instrument: Attitudes Toward Osteopathic Medicine Scale (ATOMS) and demonstrated the validity and reliability of its scores. The social desirability response bias was controlled in statistical analyses.

Results: The corrected item-total score correlations were all positive and statistically significant, and the effect sizes of item discrimination indices were large. Cronbach's coefficient alpha reliability was 0.83. Construct validity, corroborating face and content validity of the ATOMS, was supported by three components, emerged from factor analysis: "Perspectives on Osteopathic Medicine," "Osteopathic Diagnosis and Treatment," and "Holistic-Integrative Care." Correlations between ATOMS scores and scores of cognitive empathy, emotional empathy; orientation toward interprofessional collaboration; lifelong learning; and burnout were statistically significant in the expected direction, providing validity evidence for the ATOMS. Using the method of contrasted groups, significant differences in the ATOMS scores were found by gender, ethnicity, academic background, and career interest in the expected direction, supporting the validity of the ATOMS scores. National norms were developed to assess individual scores alongside national percentile ranks.

Conclusions: The ATOMS, developed in a nationwide study, supported by strong psychometric evidence for measuring orientation toward osteopathic medicine, has implications for the assessment of osteopathic medical education, patient outcomes, and admission decisions.