There is a whole field of economics doing controlled experiments (http://en.wikipedia.org/wiki/Experimental_economics http://en.wikipedia.org/wiki/Experimental_

There is a whole field of economics doing controlled experiments (http://en.wikipedia.org/wiki/Experimental_economics http://en.wikipedia.org/wiki/Experimental_economics). Most of the behavioural economics is derived from evidence from these. Otherwise, a lot of care is taken to identify causal relationships in economics (e.g. thorugh instrumenting explanatory variables).