Assessing the relative costs and benefits of reform in education is also difficult because of the large number of intervening factors that can influence the nature, size and distribution of any improvements. The investment may be expensive over the long term, while in the short term it is rarely possible to predict clear, identifiable results from new policies, especially given the time lags between implementation and effect. Teachers also tend to command greater public trust than politicians, so any resistance to reform on their part is likely to be effective. Even when parents have a poor opinion of the education system, they will generally view their children's school and its teachers positively.