Which of the following best defines epidemiology?

Epidemiology is best defined as the study that focuses on the distribution and determinants of health-related states or events, particularly diseases in populations. The correct answer encompasses both aspects of epidemiology: distribution, which refers to how diseases are spread across populations, and determinants, which includes the various factors that influence the occurrence and spread of diseases.

This definition is important because it highlights the dual focus of epidemiology on not only where diseases occur and their prevalence but also on the underlying factors that contribute to their frequency. This understanding allows public health professionals to identify at-risk populations and design interventions to reduce disease incidence.

The other choices, while related to aspects of epidemiology, are incomplete. For example, focusing solely on etiology limits the understanding to causes without addressing how widespread these causes are or other contributing factors. Similarly, stating only the determinants of frequency misses the crucial element of distribution. Lastly, an emphasis on risk factors narrows the view to specific elements without considering the broader patterns and relationships within entire populations. Thus, the holistic definition provided in the correct answer is foundational for effective public health practice.