The sole purpose of experimental research is to study causal links: to assess whether a given factor X has an impact on another factor Y, or whether changes in one variable produce changes in another. The simplest studies seek only to ascertain whether or not there is a direct link between the two factors. More complex studies seek, in addition, to assess the magnitude or importance of the effect produced (the size of the effect) and even the relative importance of the effect, that is, relative to other factors that also produce a similar impact. Experimental social research is thus relatively narrow, or focused, in the type of information it produces, but it can provide more definitive answers to questions about causal links than do other types of study, and is hence essential for the development of soundly based explanations of social events, behaviour and attitudes.