While contribution analysis provides a basis for making causal claims and understanding how and why change occurs, it does not on its own estimate the relative importance, much less the size, of the causal factors at work.
In this CDI Practice Paper written by John Mayne, we discuss ways of assessing the relative importance of such causal factors, while arguing that there are likely no quantitative answers to the question. Rather, there is a need to carefully articulate the relative importance question, decide which causal factors one wants to compare, and to decide how one wants to interpret ‘importance’. A variety of perspectives are possible: perceived influence, the roles played by the factors, the funds expended, and the extent of the constraints to change. All are plausible ways of assessing the relative importance of causal factors.