Virginia Fortna of Columbia University, however, holds that peacekeeping interventions actually do substantively matter following the end of a civil war. She claims that selection bias, where opponents point only to failed peacekeeping interventions and do not compare these missions to those situations where interventions do not occur, is partly to blame for criticisms. Fortna says that peacekeeping missions rarely go into easily resolvable situations while they are sent into tougher, more risky post war situations where missions are more likely to fail, and peace agreements are unlikely to be committed to. When all factors of a certain peacekeeping case study are properly considered, Fortna shows that peacekeeping missions do in fact help increase the chances of sustained peace after a civil war.