ABSTRACT
This chapter introduces the basic inference principle that information about a pop-
ulation can be obtained using a sample from that population. After discussing the
concepts of population and sample we interpret this principle in the context of bio-
statistics, where the goal is typically to understand and improve the health of a pop-
ulation. The importance of using samples that are representative of the population is
discussed, which requires the notion of random sampling and the concept of proba-
bility. Key probability concepts are then reviewed, including the relative frequency
interpretation that forms the basis of the standard approach to statistical inference.
We review the common ways of obtaining samples in biostatistics, including prospec-
tive, retrospective and cross-sectional samples, and discuss the concepts of sampling
variation and bias. Two of the most important measures of population health, risk
and prevalence, are defined in terms of probability and are used to illustrate random
sampling concepts throughout the chapter.
