This book is about a particular set of models, called statistics, which social and behavioral scientists have found extremely useful. In fact, most of what social scientists know about the world rests on the foundations of statistical models. It is important, therefore, that social science students understand both the reasoning behind the models, and their application in the world. A model is a representation containing the essential structure of some object or event in the real world. In either form, certain characteristics are present by the nature of the definition of a model.
Models are necessarily incomplete.
Because it is a representation, no model includes every aspect of the real world. If it did, it would no longer be a model. These assumptions are about what is necessary or important to explain the phenomena. For example, a behavioral scientist might wish to model the time it takes a rat to run a maze. In creating the model the scientist might include such factors as how hungry the rat was, how often the rat had previously run the maze, and the activity level of the rat during the previous day.