In an IAM designed for cost–benefit analysis, the costs and benefits of impacts, adaptation and mitigation are converted into monetary estimates. Some view the monetization of costs and benefits as controversial (see Economic impacts of climate change#Aggregate impacts). The "optimal" levels of mitigation and adaptation are then resolved by comparing the marginal costs of action with the marginal benefits of avoided climate change damages (Toth "et al.", 2001:654). The decision over what "optimal" is depends on subjective value judgements made by the author of the study (Azar, 1998).