An increased understanding of classical and operant conditioning has led to the development of treatments and therapies for serious mental disorders. For example, token economies have been used as a way of dealing with offending behaviour: inmates who carry out socially-desirable behaviour (such as tidying their cell and avoiding conflicts) receive tokens (secondary reinforcers) which can be traded for privileges (primary reinforcers), such as extra TV-time. Therefore, behaviourist principles have had positive impacts on the lives of many.