ABSTRACT
This book concerns making inferences about causal effects based on observational data using genetic instrumental variables, a concept known as Mendelian randomization. In this chapter, we introduce the basic idea of Mendelian randomization, giving examples of when the approach can be used and why it may be useful. We aim in this chapter only to give a flavour of the approach; details about its conditions and requirements are reserved for later chapters. Although the examples given in this book are mainly in the context of epidemiology, Mendelian randomization can address questions in a variety of fields of study, and the majority of the material in this book is equally relevant to problems in different research areas.
