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. Fig.1
