Epidemiology is defined as the study of:

The correct answer is focused on the core principles of epidemiology, which is fundamentally concerned with understanding how health and disease conditions are distributed within populations and what factors influence these patterns. Epidemiology examines both the distribution—how often diseases occur in different groups of people and why—and the determinants, which include a wide array of factors such as biological, environmental, social, and behavioral influences that can affect health outcomes.

By studying these aspects, epidemiologists can identify risk factors for disease, evaluate the effectiveness of interventions, and inform public health policy. This comprehensive perspective reflects an understanding that health is influenced by a complex interplay of various elements.

The other options, while relevant to aspects of health, do not encapsulate the full scope of what epidemiology encompasses. For instance, focusing solely on diseases, their causes, and treatments narrows the field to a medical perspective, excluding broader determinants and distributional patterns. Similarly, concentrating on specific populations or social environments limits the comprehensive analysis that epidemiology seeks to achieve.