Controlling variables in social systems - A structural modelling approach

Determining the variables to be controlled for is usually a major problem in the social sciences when analyzing possible causal relations. A structural modelling approach, having recourse to directed acyclic graphs, is presented here as a consistent framework for determining a coherent set of guidelines when deciding what variables should be controlled. Two rules are developed for determining control variables when studying respectively the direct and the total effects of a cause on an outcome. An application to contraceptive use in urban Africa is given as an example. Our approach for determining control variables is simpler and more comprehensive than alternative ones based on Pearl’s back-door criterion.