英国研究人员说，一项对86年内项目绩效新利luck的全球新研究证实，根深蒂固的乐观偏见导致基于预测的成本效益分析“如此误导，以至于比毫无价值。”他们补充说，尽管建筑技术和实践已经发展了几十年，但成本效益分析的失败“在时间和时间之间似乎是普遍的”。

牛津大学的萨伊德大学商学院的研究作者说，在行为科学的出现之前很久就发展了“成本效益理论和实践……尚未适应其关于偏见的性质和原因的发现”。新利luck结果，他们发现各种项目类型的福利成本比率继续被高估了50％至200％。

为了改善项目评估，研究人员呼吁通过系统地参考以前项目的实际绩效，激励预报员以奖励和惩罚来激励预报员，并完成独立的审核。18luck官网他们还主张将分析结果整合到现实生活中的民主决策过程中，“除了成本效益分析的结果以外，其他问题”。

The study, "The Cost-Benefit Fallacy: Why Cost-Benefit Analysis Is Broken and How to Fix It" is based on validated data on costs and benefits of 2,062 public projects built between 1927 and 2013 in 104 developed and developing nations on six continents, mostly in the US and Europe. Projects included bridges, buildings, bus rapid transit, dams, power plants, rail, roads and tunnels.

Researchers say "strong and consistent" biases led to cost overruns not being compensated by benefit overruns, "but quite the opposite, on average." In addition, projects with large average cost overruns "tend to have large average benefit shortfalls," the study says.

“理性主义者希望人类通过学习会随着时间的流逝而改善。但是，对于行为科学家而言，不是很多。1927年，人们的大脑与1960年和2013年相同，具有相同的偏见，因此他们产生了相同的不准确性，数据显示，”商学院主要计划管理主席研究负责人本特·弗洛夫·弗吉格（Bent Flyvbjerg）说。

Cost forecasts were found to be highly inaccurate and biased with average overruns ranging from 24% for highways to 85% for dams. Benefit forecasts for bridges, buildings, power plants and roads were "fairly accurate,". but average benefit shortfalls for bus rapid transit and rail projects were 58% and 34%, respectively.

However, in about 20% of cases, underforecasting of benefits more than compensated for actual cost overruns. Denmark's Great Belt toll-road bridge, for example, had a 90% benefit overrun, double that of the cost forecast. The researchers caution that the number of benefit samples for most investment types is small.

Overoptimism bias lies behind what the researchers call "the cost-benefit fallacy." They cite behavioral science evidence that planners and managers repeatedly underestimate the importance of schedules, geology, prices, scope changes and complexity and overestimate mitigation measures.

他们说：“成本效益预测的问题不是错误，而是偏见。”“只要我们允许自己被乐观偏见，过度自信偏见，概率忽视和其他行为偏见而蒙蔽，我们将不断再现成本效益的谬误。”