Chronic obstructive pulmonary disease (COPD) is one of the growing chronic respiratory diseases and is now a major cause of morbidity and mortality. Acute exacerbations have a negative impact on health related quality of life of COPD patients, survival rates, pulmonary function and utilization of health-care resources. The present application discloses an apparatus (100), system (1400), method (200), and computer program for assessing a risk of an exacerbation and/or hospitalization of a subject. To this extent, time-dependent activity data is Fourier-transformed to frequency space to obtain frequency-dependent activity data. Next, a moment of said frequency-dependent activity data is computed. Finally, a risk of said exacerbation and/or hospitalization of said subject to occur is assessed based on said moment.
