From the preface: "Professional military education (PME) is provided to Air Force officers at several points throughout their careers. All officers at the rank of major or lieutenant colonel who intend to continue in the Air Force are expected to complete a command and staff college (officers with the rank of major) and a war college (officers with the rank of lieutenant colonel). These colleges are offered by the Air Force through its Air University, at the other U.S. military services colleges or U.S. joint-service colleges, and at select international military institutions. The majority of officers complete these requirements through distance learning (DL); however, a select few spend one or two years away from their regularly assigned duties to attend these in-residence educational experiences. In addition, some officers are selected to attend a year at smaller fellowship programs offered at various public and private universities and other organizations. These officers spend a year participating in a fellowship and complete their command and staff college and war college requirements through distance learning. Senior Air Force leadership has in recent years observed that there is an apparent imbalance in the assignment of Air Force officers to specific PME programs. Notably, a greater proportion of officers who were ranked lower by the central developmental education board are assigned to PME at Air University than those higher on the central developmental education board rankings. Although there is speculation about why this occurs, the actual reasons are unknown."