The Fundamentals of Political Science Research

Researchers aspire to draw conclusions about the entire population of cases that are relevant to a particular research question. However, in almost all research situations, they must rely on data from only a sample of those cases to do so. In this chapter, we lay the foundation for how researchers make inferences about a population of cases while only observing a sample of data. This foundation rests on probability theory, which we introduce here with extensive examples. We conclude the chapter with an example familiar to political science students – namely, the “plus-or-minus” error figures in presidential approval polls, showing where such figures come from and how they illustrate the principles of building bridges from samples we know about with certainty to the underlying population of interest.