General English

General Science

  • noun the ability to act or produce something with a minimum of waste, expense or unnecessary effort


  • noun the ratio of the energy delivered by a machine to the energy supplied for its operation

Cars & Driving

  • noun the performance of a mechanical device or system, especially with regard to the amount of energy used


  • The ratio of actual performance to theoretical maximum performance.


  • noun the ability to work well or to produce the right result or the right work quickly. There are various types of efficiency: productive efficiency is where goods and services are produced at the lowest cost; allocative efficiency is where resources are allocated to producing goods and services in the most efficient way; distributional efficiency is where the distribution of goods and services to consumers is carried out in the most efficient way.


  • The ratio of the useful power or energy output of a device or system, to its total power or energy input. Also called output efficiency (2), or power efficiency (1).
  • The proportion of the audio frequency electrical power input to a speaker which is converted into acoustic energy. Efficiency may be measured, for instance, by driving a speaker with a power input of 1 watt, and measuring its output, in decibels, at a distance of 1 meter. Also called speaker efficiency, loudspeaker efficiency, sensitivity (4), or power efficiency (2).

Health Economics

  • (written as Efficiency)

    In a restrictive sense, efficiency is defined either as minimizing the opportunity cost of attaining a given output or as maximizing the output for a given opportunity cost. The general term used by economists is Pareto-efficiency. This is an allocation of resources such that it is not possible to reallocate any of them without imposing uncompensated losses of utility on some individual. A variant is potential Pareto-efficiency, where it is not possible to reallocate resources without imposing non-compensable losses on someone (i.e. the losses may not actually be compensated). It is common to see the notion of efficiency expressed at three different levels: technical efficiency, where more inputs are not used than are technically necessary to attain a given output (there will normally be a wide variety of different combinations arising out of their substitutability); cost-efficiency or cost-effectiveness, where a given output is produced using the least-cost technically efficient combination of inputs or, conversely, output is maximized for a given level of cost (the combinations of resources here will be a subset of those deemed technically efficient); Pareto-efficiency, where output is not only technically- and cost-efficient but is also set at an efficient rate such that any diminution or increase would cause marginal cost to exceed or fall below the marginal value to consumers. Pareto-efficiency is also termed ' allocative efficiency ' (a somewhat unhelpful term since all three ideas of efficiency are about resource allocation). The first two ideas concern the allocation of inputs to outputs; the third concerns the allocation of outputs to consumers, clients or users.

    A variant idea of efficiency arises under what is known as extra-- welfarism. With this (rather than general utility or welfare) as the framework, the maximand may be whatever the analyst or policy-maker selects as appropriate. In health policy, health or health gain are common objectives. In such cases, health may be set as the maximand and efficiency implies either achieving a given overall level of health in the population at the least opportunity cost or, for a given set of resources, maximizing their impact on overall health. The idea of 'overall' health implies, of course, some means of 'adding up' the health of individual people, which will entail some distributional value judgments concerning the weight each is to have. In extra-welfarism, it seems better not to extend the idea of efficiency to achieve an efficient distribution of outputs to clients, leaving this as a matter of equity, to be determined in other ways and by other criteria. Needless to say, equity objectives can themselves also be achieved with varying degrees of efficiency!

    It should be plain that 'efficiency' is an inherently normative term. It tends to commend itself to economists, who do not always stop to think that whether it is good to be efficient may depend on what it is one is being efficient at doing. An efficiently run torture chamber scarcely commends itself; indeed it were better for such places to be inefficient than efficient. Nevertheless, the economists' concept of efficiency is pretty completely worked out and complements work in related fields such as epidemiology.


  • noun the ability to make a physical movement with a minimum of unnecessary effort