Causal instrumental variables and interventions

The aim of this paper is to introduce the instrumental variables technique to the discussion about causal inference in econometrics. I show that it may lead to causally incorrect conclusions unless some fairly strong causal background assumptions are made, assumptions which are usually left implicit by econometricians. These assumptions are very similar to, albeit not identical with, James Woodward's definition of an 'intervention'. I discuss similarities and differences of the two points of view and argue that-understood as a practical method of causal inference-the set presented here is superior.