In real life there are many force that affect the outcome(s) of an event. In the social sciences, a particular event seldom occurs for a single reason. It is the multiplicity of factors that determine the outcome of an event. It is true that some relationships are easy to understand while there are others more complex and difficult. In almost every relationship, simple or complex, most outcomes are a result of the interplay of a multiplicity of interacting factors. In order to reliably establish a cause-and-effect relationship, it is therefore important to design a study in such a way that enables you to link cause(s) with the effect(s) and vice versa. It is important for such studies to be able to isolate the effect of all other factors that are of no interest to you as a researcher but have a bearing on the outcomes. The concept of control implies that, in exploring causality in relation to two variables, you set up your study in such a way that it either minimizes or quantifies (as it is impossible to eliminate) the effects of factors, other than the cause variable, affecting the relationship. This can be achieved to a large extent in the physical sciences, as most of the research is done in a laboratory. However, in the social sciences it is extremely difficult as research is carried out on issues relating to human beings living in society, where such controls are impossible. Therefore, in the social sciences, as you cannot control external factors, you attempt to quantify their impact.