Cost overrun

A cost overrun, also known as a cost increase, underrated or budget overrun, involves unexpected costs incurred in excess of budgeted amounts due to an underestimation of the actual cost during budgeting. Cost overrun should be distinguished from cost escalation, which is used to express an anticipated growth in a budgeted cost due to factors such as inflation.

Cost overrun is common in infrastructure, building, and technology projects. For IT projects, a 2004 industry study by the Standish Group found an average cost overrun of 43 percent; 71 percent of projects came in over budget, exceeded time estimates, and had estimated too narrow a scope; and total waste was estimated at $55 billion per year in the US alone.

Many major construction projects have incurred cost overruns; cost estimates used to decide whether important transportation infrastructure should be built can mislead grossly and systematically.

Recent works by Ahiaga-Dagbui and Smith suggests a rethink of what is traditionally referred to as overruns in construction. They attempt to make a distinction between the often conflated causes of construction cost underestimation and eventual cost overruns. Critical to their argument is the point of reference for measuring cost overruns. Whereas some measure the size of cost overruns as the difference between cost at the time of decision to build and final completion costs, others measure the size of overruns as the difference between cost at contract award and final completion cost.This leads to a wide range in the size of overruns reported in different studies.

Three types of explanation for cost overrun exist: technical, psychological, and political-economic. Technical explanations account for cost overrun in terms of imperfect forecasting techniques, inadequate data, etc. Psychological explanations account for overrun in terms of optimism bias with forecasters. Scope creep, where the requirements or targets rises during the project, is common. Finally, political-economic explanations see overrun as the result of strategic misrepresentation of scope or budgets. Historically, political explanations for cost overrun have been seen to be the most dominant. In the USA, the architectural firm Home Architects has attributed this to a human trait they call "Psychology of Construction Cost Denial", regarding the cost inflation of custom homes.

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