Preface

Understanding human health—defined by the World Health Organization (WHO) as a “state of complete physical, mental, and social well-being, and not merely the absence of disease or infirmity”ⁱ—is vital. Why are these people sick but those people aren’t? What can we do to improve health for everyone? Improved health in turn leads to gains in economic, social, educational, and other arenas, all of which are necessary for a successful, functioning society.

Unfortunately, to understand human health, we must study humans—and humans are extremely difficult to study. Unlike laboratory-based sciences, where all conditions are under the control of the scientist, conducting scientific studies with human participants includes a host of complications and potential stumbling blocks. First and foremost, humans do not exist in controlled settings like laboratories. Each person has their own job, their own preferred foods, their own sleep schedule, their own hobbies, their own genetics, their own stress levels, their own set of environmental and social settings—all of which affect health. Since no two people are exactly alike, and since we cannot really tell people what to do, studying them is difficult.

Epidemiology is the set of tools we use to study human health. As such, it is not a topic itself per se, but rather a set of research methods that are then applied to other health-related topics (kinesiology, infectious disease, cardiology, child development, etc.). Epidemiology can help answer questions such as the following:

• Are dietary-based or exercise-based interventions better for preventing a second heart attack?
• Which people are at the highest risk of dying from influenza?
• Is it safe to eat raw oysters?
• Do birth control pills cause breast cancer?
• How does Zika virus spread?

An understanding of epidemiologic methods is helpful for anyone interested in human health, particularly those in public health or clinical fields. This book is written primarily for use in undergraduate introductory epidemiology classes; however, graduate students, medical students, and professionals working in public or allied health fields may also find it useful either as an introduction or as a refresher.

This book is intended to provide a basic introduction to epidemiologic methods and epidemiologic thinking. After reading this book, you should be able to read an epidemiologic study, understand what the authors did and why, and identify what they found. You will also have the tools to assess the quality of that study—how good is the evidence? What are potential sources of bias, and how might those have affected the results? This book will not teach you enough to be able to design and conduct your own epidemiologic studies—that level of understanding requires several years of specialized training. However, being able to read and understand the scientific literature about human health will allow you to apply that understanding to your own work in a nuanced, sophisticated way.

It will also allow you to be a confident consumer of the news—how many times have you seen a headline about some new, health-related study and wondered if it could possibly be “real”? Now you will be able to assess for yourself whether the touted new study should change your behavior or not. For instance, for many years we were told that low levels of alcohol consumption, particularly of red wine, were beneficial.ⁱⁱ Then during the summer of 2018, the WHO released a statement saying that no, all alcohol consumption is harmful.ⁱⁱⁱ What should you do? Is a glass of wine a day a good idea or not? This book will provide the tools necessary for you to be able to assess the epidemiologic evidence and decide for yourself.