In the next few chapters, we study enough probability that allows us to assign certain reasonable probability models to important cases. Often we do not know everything about these models; that frequently have unknown parameters. Thus, we must observe the results of several trials of the experiment to make further inferences about the models; in particular, we must estimate the unknown parameter(s). This process of refining a model by using the data is referred to as making a statistical inference and is the focus of the latter part of the text.