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Efficiency is the extent to which time, effort, or cost is well-used for the intended task or purpose. It often comprises specifically the capability of a specific application of effort to produce a specific outcome effectively with a minimum amount or quantity of waste, expense, or unnecessary effort. "Efficiency" has widely varying meanings in different disciplines.
The term "efficient" is very much confused and misused instead of the term "effective". In general, efficiency is a measurable concept, quantitatively determined by the ratio of output to input. "Effectiveness", is a relatively vague, non-quantitative concept, mainly concerned with achieving objectives. In several of these cases, efficiency can be expressed as a result as percentage of what ideally could be expected, hence with 100% as ideal case. This does not always apply, not even in all cases where efficiency can be assigned a numerical value, e.g. not for specific impulse.
A simple way of distinguishing between efficiency and effectiveness is the saying, "Efficiency is doing things right, while effectiveness is doing the right things." This is based on the premise that selection of objectives of a process is just as important as the quality of that process.
For example, one may measure how directly two objects are communicating: downloading music directly from a computer to a mobile device is more efficient than using a mobile device's microphone to record music sounds that come from a computer's speakers.
Efficiency is often measured as the ratio r=P/C, the amount P of some valuable output produced per amount C of valuable resources consumed.This may correspond to a percentage if products and consumables are quantified in compatible units, and if consumables are transformed into products via a conservative process. For example, in the analysis of the energy conversion efficiency of heat engines in thermodynamics, the product P may be the amount of useful work output, while the consumable C is the amount of high-temperature heat input. Due to the conservation of energy, P can never be greater than C, and so the efficiency r is never greater than 100% (and in fact must be even less at finite temperatures).
In science and technology
- Useful work per quantity of energy, mechanical advantage over ideal mechanical advantage, often denoted by the Greek lowercase letter η (Eta):
- Efficient energy use, the objective of maximising efficiency
- Lift-to-drag ratio
- Faraday efficiency, electrolysis
- Quantum efficiency, a measure of sensitivity of a photosensitive device
- Grating efficiency, a generalization of the reflectance of a mirror, extended to a diffraction grating
- Productivity improving technologies (historical)
- Economic efficiency, the extent to which waste or other undesirable features are avoided
- Market efficiency, the extent to which a given market resembles the ideal of an efficient market
- Pareto efficiency, a state of its being impossible to make one individual better off, without making any other individual worse off
- Kaldor-Hicks efficiency, a less stringent version of Pareto efficiency
- Allocative efficiency, the optimal distribution of goods
- Efficiency wages, paying workers more than the market rate for increased productivity
- Business efficiency, revenues relative to expenses, etc.
- Efficiency Movement, of the Progressive Era (1890–1932), advocated efficiency in the economy, society and government
In other sciences
- Efficiency (statistics), a measure of desirability of an estimator
- Material efficiency, compares material requirements between construction projects or physical processes
- Administrative efficiency, measuring transparency within public authorities and simplicity of rules and procedures for citizens and businesses
- Efficiency in Flora, Fauna and other natural phenomenons:
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