Cost benefit analysis (CBA), sometimes called benefit–cost analysis (BCA), is a systematic process for calculating and comparing benefits and costs of a project, decision or government policy (hereafter, "project"). CBA has two purposes:
- To determine if it is a sound investment/decision (justification/feasibility),
- To provide a basis for comparing projects. It involves comparing the total expected cost of each option against the total expected benefits, to see whether the benefits outweigh the costs, and by how much.
CBA is related to, but distinct from cost-effectiveness analysis. In CBA, benefits and costs are expressed in monetary terms, and are adjusted for the time value of money, so that all flows of benefits and flows of project costs over time (which tend to occur at different points in time) are expressed on a common basis in terms of their "net present value."
Closely related, but slightly different, formal techniques include cost-effectiveness analysis, cost–utility analysis, economic impact analysis, fiscal impact analysis and Social return on investment (SROI) analysis.
Cost–benefit analysis is often used by governments and other organizations, such as private sector businesses, to evaluate the desirability of a given policy. It is an analysis of the expected balance of benefits and costs, including an account of foregone alternatives and the status quo. CBA helps predict whether the benefits of a policy outweigh its costs, and by how much relative to other alternatives (i.e. one can rank alternate policies in terms of the cost-benefit ratio). Generally, accurate cost-benefit analysis identifies choices that increase welfare from a utilitarian perspective. Assuming an accurate CBA, changing the status quo by implementing the alternative with the lowest cost-benefit ratio can improve Pareto efficiency. An analyst using CBA should recognize that perfect evaluation of all present and future costs and benefits is difficult, and while CBA can offer a well-educated estimate of the best alternative, perfection in terms of economic efficiency and social welfare are not guaranteed.
The following is a list of steps that comprise a generic cost-benefit analysis.
- List alternative projects/programs.
- List stakeholders.
- Select measurement(s) and measure all cost/benefit elements.
- Predict outcome of cost and benefits over relevant time period.
- Convert all costs and benefits into a common currency.
- Apply discount rate.
- Calculate net present value of project options.
- Perform sensitivity analysis.
- Adopt recommended choice.
CBA attempts to measure the positive or negative consequences of a project, which may include:
- Effects on users or participants
- Effects on non-users or non-participants
- Externality effects
- Option value or other social benefits.
A similar breakdown is employed in environmental analysis of total economic value. Both costs and benefits can be diverse. Financial costs tend to be most thoroughly represented in cost-benefit analyses due to relatively abundant market data. The net benefits of a project may incorporate cost savings or public willingness to pay compensation (implying the public has no legal right to the benefits of the policy) or willingness to accept compensation (implying the public has a right to the benefits of the policy) for the welfare change resulting from the policy. The guiding principle of evaluating benefits is to list all (categories of) parties affected by an intervention and add the (positive or negative) value, usually monetary, that they ascribe to its effect on their welfare.
The actual compensation an individual would require to have their welfare unchanged by a policy is inexact at best. Surveys (stated preference techniques) or market behavior (revealed preference techniques) are often used to estimate the compensation associated with a policy; however, survey respondents often have strong incentives to misreport their true preferences and market behavior does not provide any information about important non-market welfare impacts.
One controversy is valuing a human life, e.g. when assessing road safety measures or life-saving medicines. However, this can sometimes be avoided by using the related technique of cost-utility analysis, in which benefits are expressed in non-monetary units such as quality-adjusted life years. For example, road safety can be measured in terms of cost per life saved, without formally placing a financial value on the life. However, such non-monetary metrics have limited usefulness for evaluating policies with substantially different outcomes. Additionally, many other benefits may accrue from the policy, and metrics such as 'cost per life saved' may lead to a substantially different ranking of alternatives than traditional cost-benefit analysis.
Another controversy is valuing the environment, which in the 21st century is typically assessed by valuing ecosystem services to humans, such as air and water quality and pollution. Monetary values may also be assigned to other intangible effects such as business reputation, market penetration, or long-term enterprise strategy alignment.
Time and Discounting 
CBA usually tries to put all relevant costs and benefits on a common temporal footing using time value of money calculations. This is often done by converting the future expected streams of costs and benefits into a present value amount using a discount rate. Empirical studies and a technical framework suggest that in reality, people do discount the future like this.
The choice of discount rate is subjective. A smaller rate values future generations equally with the current generation. Larger rates (e.g. a market rate of return) reflects humans' attraction to time inconsistency—valuing money that they receive today more than money they get in the future. The choice makes a large difference in assessing interventions with long-term effects, such as those affecting climate change. One issue is the equity premium puzzle, in which long-term returns on equities may be rather higher than they should be. If so then arguably market rates of return should not be used to determine a discount rate, as doing so would have the effect of undervaluing the distant future (e.g. climate change).
Risk and uncertainty 
Risk associated with project outcomes is usually handled using probability theory. This can be factored into the discount rate (to have uncertainty increasing over time), but is usually considered separately. Particular consideration is often given to risk aversion—the irrational preference for avoiding loss over achieving gain. Expected return calculations does not account for the detrimental effect of uncertainty.
Uncertainty in CBA parameters (as opposed to risk of project failure etc.) can be evaluated using a sensitivity analysis, which shows how results respond to parameter changes. Alternatively a more formal risk analysis can be undertaken using Monte Carlo simulations.
The concept of CBA dates back to an 1848 article by Jules Dupuit and was formalized in subsequent works by Alfred Marshall. The Corps of Engineers initiated the use of CBA in the US, after the Federal Navigation Act of 1936 effectively required cost–benefit analysis for proposed federal waterway infrastructure. The Flood Control Act of 1939 was instrumental in establishing CBA as federal policy. It demanded that "the benefits to whomever they accrue [be] in excess of the estimated costs.
Public Policy 
The application for broader public policy started from the work of Otto Eckstein, who in 1958 laid out a welfare economics foundation for CBA and its application for water resource development. Over the 1960s, CBA was applied in the US for water quality, recreation travel and land conservation. During this period, the concept of option value was developed to represent the non-tangible value of preserving resources such as national parks.
CBA was later expanded to address both intangible and tangible benefits of public policies relating to mental illness, substance abuse, college education and chemical waste policies. In the US, the National Environmental Policy Act of 1969 first required the application of CBA for regulatory programs, and since then, other governments have enacted similar rules. Government guidebooks for the application of CBA to public policies include the Canadian guide for regulatory analysis, Australian guide for regulation and finance, US guide for health care programs, and US guide for emergency management programs.
Transportation Investment 
CBA application for transport investment started in the UK, with the M1 motorway project in 1960. It was later applied on many projects including London Underground's Victoria Line. Later, the New Approach to Appraisal (NATA) was introduced by the then Department for Transport, Environment and the Regions. This presented cost–benefit results and detailed environmental impact assessments in a balanced way. NATA was first applied to national road schemes in the 1998 Roads Review but subsequently rolled out to all transport modes. As of 2011 it was a cornerstone of transport appraisal in the UK and is maintained and developed by the Department for Transport.
The EU's 'Developing Harmonised European Approaches for Transport Costing and Project Assessment' (HEATCO) project, part of its Sixth Framework Programme, reviewed transport appraisal guidance across EU member states and found that significant differences exist between countries. HEATCO's aim was to develop guidelines to harmonise transport appraisal practice across the EU.
In the US, both federal and state transport departments commonly apply CBA, using a variety of available software tools including HERS, BCA.Net, StatBenCost, Cal-BC, and TREDIS. Guides are available from the Federal Highway Administration, Federal Aviation Administration, Minnesota Department of Transportation, California Department of Transportation (Caltrans), and the Transportation Research Board Transportation Economics Committee.
The value of a cost–benefit analysis depends on the accuracy of the individual cost and benefit estimates. Comparative studies indicate that such estimates are often flawed, preventing improvements in Pareto and Kaldor-Hicks efficiency. Causes of these inaccuracies include:
- Overreliance on data from past projects (often differing markedly in function or size and the skill levels of the team members)
- Use of subjective impressions by assessment team members
- Inappropriate use of heuristics to derive money cost of the intangible elements
- Confirmation bias among project supporters (looking for reasons to proceed).
Interest groups may attempt to include or exclude significant costs from an analysis to influence the outcome.
In the case of the Ford Pinto (where, because of design flaws, the Pinto was liable to burst into flames in a rear-impact collision), the company's decision was not to issue a recall. Ford's cost–benefit analysis had estimated that based on the number of cars in use and the probable accident rate, deaths due to the design flaw would cost it about $49.5 million to settle wrongful death lawsuits versus recall costs of $137.5 million. Ford overlooked (or considered insignificant) the costs of the negative publicity that would result, which forced a recall and damaged sales.
In health economics, some analysts think cost–benefit analysis can be an inadequate measure because willingness-to-pay methods of determining the value of human life can be influenced by income level. They support use of variants such as cost–utility analysis and quality-adjusted life year to analyze the effects of health policies.
In environmental and occupational health regulation, it has been argued that if modern cost-benefit analyses had been applied prospectively to decisions such as whether to mandate the removal of lead from gasoline, build the Hoover Dam in the Grand Canyon, and regulate workers' exposure to vinyl chloride, these measures would not have been implemented even though they are considered to be highly successful in retrospect. The Clean Air Act has been cited in retrospective studies as a case where benefits exceeded costs, but the knowledge of the benefits (attributable largely to the benefits of reducing particulate pollution) was not available until many years later.
See also 
- Guns versus butter model
- Have one's cake and eat it too
- Opportunity cost
- Tax choice
- There ain't no such thing as a free lunch
- [dead link]
- Stephanie Riegg Cellini, James Edwin Kee. COST-EFFECTIVENESS AND COST-BENEFIT ANALYSIS. Chapter 21.http://home.gwu.edu/~scellini/CelliniKee21.pdf
- Weimer, D., Vining, A. Policy Analysis: Concepts and Practice. Fourth Edition. 2005.
- Boardman, N. E. (2006). Cost-benefit analysis, concepts and practice. (3 ed.). Upper Saddle River, NJ: Prentice Hall
- Campbell and Brown (2003) Ch. 8 provides a useful discussion of non-market valuation methods for CBA.http://www.uq.edu.au/economics/bca/
- Dunn, William N. "Public Policy Analysis: an Introduction." Longman (2009)
- R.G. Newell(2003). Journal of Environmental Economics and Management. http://www.nicholas.duke.edu/people/faculty/newell/jeem%20discount.pdf.
- Campbell and Brown (2003) Ch. 9 provides a useful discussion of sensitivity analysis and risk modelling in CBA.http://www.uq.edu.au/economics/bca/
- History of Benefit-Cost Analysis, Proceedings of the 2006 Cost Benefit Conference 
- "Google book extract from ''Cases in Public Policy Analysis'' By George M. Guess, Paul G. Farnham". Books.google.com. Retrieved 2013-04-21.
- Eckstein, Otto, 1958. Water Resource Development: The Economics of Project Evaluation, Harvard University Press, Cambridge.
- Kneese, A.V., 1964. The Economics of Regional Water Quality Management, Johns Hopkins Press, Baltimore.
- Clawson M and J.L. Knetsch, 1966. Economics of Outdoor Recreation, Johns Hopkins Press, Baltimore.
- Krutilla, J.V., 1967. "Conservation Reconsidered," American Economic Review, 57.
- Weisbrod, Burton A., 1964. "Collective-Consumption Services of Individual-Consumption Goods," Quarterly Journal of Economics, 78(3).
- Weisbrod, Burton A., 1981. "Benefit-Cost Analysis of a Controlled Experiment: Treating the Mentally Ill," Journal of Human Resources, 16(4).
- Plotnick, Robert D., 1994. "Applying Benefit-Cost Analysis to Substance Abuse Prevention Programs," International Journal of the Addictions, 29(3).
- Weisbrod, Burton A. and W. Lee Hansen, 1969. Benefits, Costs, and Finance of Public Higher Education, Markham Publishing.
- Moll, K. S. et al, 1975. "Hazardous wastes: A Risk-Benefit Framework Applied to Cadmium and Asbestos." Stanford Research Institute, Menlo Park, CA.
- Canadian Cost-Benefit Guide: Regulatory Proposals, Treasury Canada, 2007. 
- Australian Government, 2006. Introduction to Cost-Benefit Analysis and Alternative Evaluation Methodologies and Handbook of Cost-Benefit Analysis, Finance Circular 2006/01. http://www.finance.gov.au/publications/finance-circulars/2006/01.html
- US Department of Health and Human Services, 1993. Feasibility, Alternatives, And Cost/Benefit Analysis Guide, Administration for Children and Families, and Health Care Finance Administration. http://www.acf.hhs.gov/programs/cb/systems/sacwis/cbaguide/index.htm
- Federal Emergency Management Administration, 1022. Guide to Benefit Cost Analysis. http://www.fema.gov/government/grant/bca.shtm
- [dead link]
- "HEATCO project site". Heatco.ier.uni-stuttgart.de. Retrieved 2013-04-21.
-  Guide to Cost-Benefit Analysis of Major Projects. Evaluation Unit, DG Regional Policy, European Commission, 2008.
- Guide to Benefit-Cost Analysis in Transport Canada. Transport Canada. Economic Evaluation Branch, Transport Canada, Ottawa, 1994 
- US Federal Highway Administration: Economic Analysis Primer: Benefit-Cost Analysis 2003 
- US Federal Highway Administration: Cost-Benefit Forecasting Toolbox for Highways, Circa 2001 
- US Federal Aviation Administration: Airport Benefit-Cost Analysis Guidance, 1999  
- Minnesota Department of Transportation: Benefit Cost Analysis. MN DOT Office of Investment Management 
- California Department of Transportation: Benefit-Cost Analysis Guide for Transportation Planning 
- Transportation Research Board, Transportation Economics Committee: Transportation Benefit-Cost Analysis 
- [author missing] (1935). "Spokane Daily Chronicle". news.google.com. Retrieved 29 December 2011.
- Phelps,Charles. Health Economics. 4th Edition. 2009.
- Ackerman et al. (2005). Applying Cost-Benefit to Past Decisions: Was environmental protection ever a good idea. Administrative Law Review.
Further reading 
- Ascott, Elizabeth. 2006. Benefit Cost Analysis of Wonderworld Drive Overpass in San Marcos, Texas. Applied Research Project. , Texas State University
- Benefit/Cost Analysis: Introduction. Mankato State University. undated. 
- Campbell, Harry and Brown, Richard (2003) Benefit-Cost Analysis: Financial and Economic Appraisal Using Spreadsheets. Cambridge University Press 
- Chakravarty, Sukhamoy (1987). "cost-benefit analysis," The New Palgrave: A Dictionary of Economics, v. 1, pp. 687–90.
- Dupuit, Jules. "On the Measurement of the Utility of Public Works" in Readings in Welfare Economics, ed. Kenneth J. Arrow and Tibor Scitovsky (1969)
- Eckstein, Otto. Water-resource Development: The Economics Of Project Evaluation. Cambridge : Harvard University Press, 1958.
- Folland, Sherman, Allen C. Goodman and Miron Stano. The Economics of Heath and Health Care. Fifth ed. Pearson Prentice Hall: New Jersey, 2007. pg 83, 84.
- Ferrara, A. (2010) Cost-Benefit Analysis of Multi-Level Government: The Case of EU Cohesion Policy and US Federal Investment Policies, London and New York: Routledge.
- Frank, Robert H. "Why is Cost-Benefit Analysis so Controversial?" The Journal of Legal Studies 29, no. S2 (2000): 913-30.
- Hirshleifer, Jack. Water Supply: Economics, Technology, And Policy. Chicago: University Of Chicago Press 1960.
- Maass, Arthur., eds. Design Of Water-resource Systems: New Techniques For Relating Economic Objectives, Engineering Analysis, And Governmental Planning. Cambridge: Harvard University Press, 1962.
- McKean, Roland N. Efficiency In Government Through Systems Analysis: With Emphasis On Water Resources Development. New York: Wiley 1958.
- Portney, Paul R., Benefit-Cost Analysis, in The Library Of Economics and Liberty. 
- Proposed Practices For Economic Analysis Of River Basin Projects. Washington: [U.S. Govt. Print. Off.], 1950.
- Richardson, Henry S. "The Stupidity of the Cost-Benefit Analysis." The Journal of Legal Studies 29, no. S2 (2000): 971-1003.
- Quigley, John and Lesley Walls. "Cost-Benefit Modelling for Reliability Growth." The Journal of the Operational Research Society 54, no. 12 (2003): 1234-41.
- Sen, Amartya. "The Discipline of Cost-Benefit Analysis" The Journal of Legal Studies 29, no. S2 (2000): 931-952.
- Tevfik F. Nas, Cost-Benefit Analysis: Theory and Application (Thousand Oaks, Ca.: Sage, 1996). 
- Kosub, Jeffry, (2010) "Transitioning to a Greener Fleet: A Cost-Benefit Analysis of a Vehicle Fleet Program at the Texas General Land Office in Austin, Texas" (2010). Applied Research Projects. Texas State University. Paper 329. http://ecommons.txstate.edu/arp/329
- Benefit-Cost Analysis Center at the University of Washington's Daniel J. Evans School of Public Affairs
- Society for Benefit-Cost Analysis
- Journal of Benefit-Cost Analysis
- Cost-Benefit Analysis Course at the Harris School of Public Policy Studies
- The Environmental Valuation & Cost-Benefit Website
- Environmental Valuation & Cost-Benefit News
- Transportation Research Board, Transportation Economics Committee: Transportation Benefit-Cost Analysis
- Caltrans Guide to Benefit-Cost Analysis
- Decision Analysis in Health Care George Mason University online course offering lectures and tools for measuring cost-effectiveness in health care scenarios.
- Reports on cost-benefit analysis and the environment in Tropical countries
- Cost Benefit Knowledge Bank for Criminal Justice
- Companion website to Campbell and Brown (2003) with downloadable chapters, examples and case-studies.
- UK Military Aviation Authority Regulatory Notice MAA/RN/12/11(DG) – Cost Benefit Analysis of Potential Air Safety Measures - Principles dated 8 Nov 11