Cost-benefit analysis

Cost-benefit analysis is used to evaluate projects that generate non-financial costs and benefits by taking account of the preferences of those affected. It has applications to the provision of public goods for which preferences are not reflected in market prices. Although its quantitative results are necessarily approximate, it can sometimes provide a persuasive guide to a choice among alternatives. It is claimed that, by taking account of the strengths of preferences, cost-benefit analysis can provide a better guide to choice than can be obtained from voting.

Introduction
The function of cost-benefit analysis is to inform a decision  that is to be taken on behalf of others. Its objective is to indicate whether the decision would be consistent with the preferences of those affected. The decision-maker's rôle in cost-benefit analysis is taken to be confined to the specification of its scope and of the decision-making criterion to be adopted. The analyst's functions are to forecast the material consequences of a decision, to evaluate each consequence in light of the preferences of those that would be affected, and to aggregate the resulting valuations.

Criteria
The customary ("consequentialist") decision criterion of cost-benefit analysis uses the summation of the effects  of the expected consequences of a decision on the well-being of people within its scope. The alternative ("deontologist") decision criterion takes account of the views of those affected concerning the need to conform to predetermined rules (such as the sacredness of human life or the prohibition of interest-paying debt). To make a summation possible, a monetary cost or benefit is assigned to each of those effects. (Monetisation under the deontology criterion may be based upon the costs of socially-agreed practices that conform to the relevant rules) The summation normally used is then that of the costs and benefits of  each effect, weighted by their estimated probability of occurrence, and discounted using the estimated time preference rates of those affected. The acceptance criterion for a single project is a positive value of the resulting net present expected value of the excess of benefits over costs, and the acceptance criterion for the acceptance of one among several alternatives is that it should be the one with the  highest net present expected value.

Scope
The scope of an analysis is normally determined by the requirements of its prospective users. The evaluation of a medical procedure might, for example, be concerned solely with its effects on patients and their families, or it might also encompass effects on the  hospital or on the public at large. An evaluation of migration commissioned by a European government might or might not be required to include effects upon migrants and their families, but an evaluation commissioned by the European Union might be expected to require the inclusion of effects upon all of its inhabitants. Some users require the coverage of a longer timescale than others,  and environmental studies may even be required to encompass effects on future generations.

Reports that do not specify the scope of a quoted cost-benefit analysis are open to misinterpretation.

Valuation
The outcomes whose valuations typically figure in  cost-benefit analysis, include benefits such as the saving of time and the relief of suffering, and non-financial costs in the form of  unwelcome experiences such as injury and  exposure to noise. The monetary value to a person of such an outcome is taken to be the amount that he would be willing to pay in order to enjoy its benefits or avoid its costs. The preferred way of estimating that amount is the revealed preference method, which depends upon the observation of the subject's conduct in making free and well-informed choices. The collective valuation of an outcome can be reliably estimated from the price  that is determined by  choices made in an efficient market, a reasonable approximation to which is  often provided by organised markets for products and services (and estimates of the value of time are often derived from the wage rates ruling in the labour market ). Relevant observations of the results of such choices are not always available, however, and other observed  choices provide a less reliable basis for valuation. Estimates of the value of life derived from the payments or other benefits that are commonly accepted in return for conduct involving the risk of death, may be seriously distorted by probability blindness. If the deontological criterion is considered appropriate, the value of life may alternatively be based upon the costs of community-determined practices concerning its preservation, such as prolonged hospitalisation.

In the absence of revealed preference methods, valuation may be based upon "stated preference" assessments involving surveys of  those affected.

Metrics used in cost-benefit analyses

 * Cost per year of life saved The definition of an acceptable cost per year of life saves ranges from $50,000 to $200,000.
 * Cost of Preventing an Event (COPE) . For example, to prevent a major vascular event n a high-risk adult, the number needed to treat is 19, the number of years of treatment are 5, and the daily cost of the generic drug is 68 cents. The COPE is 19 * 5 * ( 365 * .68) which equals $23,579 in the United States.
 * Years (or months or days) of life saved. "A gain in life expectancy of a month from a preventive intervention targeted at populations at average risk and a gain of a year  from a preventive intervention targeted at populations at elevated risk can both be considered large."

Standards in conducting a cost-benefit analysis
Standards have been developed for the conduct of cost-benefit analyses  and for systematic reviews of cost-benefit analyses.

The two most common problems in publications of cost-benefit analyses are not stating the study perspective (e.g. is the cost born by the patient, health case system, or society) and not disclosing the funding source.

Difficulties in cost-benefit analyses
The costs saved by successful treatment of one disease may be offset by greater longevity leading to increased costs from other disease.

Recommendations have bee published on how to read and interpret a cost-benefit analysis.