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Introduction

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An important perspective in healthcare research is based on principles of epidemiology, which focus on the distribution and determinants of health outcomes in different populations. This information can be used to understand patterns of disease in different groups, to evaluate causative and preventive factors, and to understand the effectiveness of health policy and resource allocation. Research findings can have direct influence on decision-making related to diagnosis, prognosis, or intervention. Epidemiology involves descriptive and analytic approaches, which are appropriate for both observational and experimental designs (see Chapters 16 and 19). The purpose of this chapter is to present statistical methods for measures of disease frequency, estimates of health risks for cohort and case-control studies, and the evaluation of treatment effects in randomized trials.

The Scope of Epidemiology

Epidemiology literally began as the study of “epidemics,” concerned primarily with mortality and morbidity from acute infectious diseases. Many of the health standards we take for granted today, such as clean water supplies, treatment of sewage, and food refrigeration, can be credited to discoveries made through epidemiological investigations.Epidemiologists try to identify those who have a specific disorder, when and where the disorder developed, and what exposures are associated with its presence. Epidemiologic questions often arise out of clinical experience, laboratory findings, or public health concerns about the relationship between societal practices and disease outcomes. Through the analysis of health status indicators and population characteristics, epidemiologists try to identify and explain the causal factors in disease patterns.

As medical cures and treatments have been developed to control many of these problems, and as patterns of disease have changed, the scope of epidemiology has broadened. Today clinical epidemiology includes the study of chronic disease, disability, and health status. This approach fits with the World Health Organization’s definition of health which encompasses social, psychological and physical well-being.1

image The terms disease, disorder, and disability will be used interchangeably to represent health outcomes, recognizing the variety of conditions of interest, including illness, injury, and physical, psychological, or social dysfunction.

Descriptive Epidemiology

Descriptive epidemiologic studies are done when little is known about the occurrence or determinant of health conditions. They will often provide information that can be used to set priorities for healthcare planning and will generate hypotheses that can be studied using analytic methods. Descriptive studies may be presented as case reports, correlational studies, or cross-sectional surveys.

Person, Place, and Time

The purpose of descriptive epidemiologic studies is to describe patterns of health, disease, and disability in terms of person, place, and time.

WHO Experiences this Disorder?

Relevant characteristics might include age, sex, religion, race, cultural background, education, socioeconomic status, occupation, and so on. This is the demography of the disorder. Epidemiologists try to determine if individuals with certain characteristics ...

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