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In statistics, efficiency is a measure of quality of an estimator, of an experimental design, [1] or of a hypothesis testing procedure. [2] Essentially, a more efficient estimator needs fewer input data or observations than a less efficient one to achieve the Cramér–Rao bound.
Unlike efficacy (effectiveness), which is a unit of measurement, efficiency is a unitless number expressed as a percentage, requiring only that the input and output units be of the same type. The luminous efficiency of a light source is thus the percentage of luminous efficacy per theoretical maximum efficacy at a specific wavelength.
Efficiency is very often confused with effectiveness. In general, efficiency is a measurable concept, quantitatively determined by the ratio of useful output to total useful input. Effectiveness is the simpler concept of being able to achieve a desired result, which can be expressed quantitatively but does not usually require more complicated ...
The efficiency ratio indicates the expenses as a percentage of revenue (expenses / revenue), with a few variations – it is essentially how much a corporation or individual spends to make a dollar; entities are supposed to attempt minimizing efficiency ratios (reducing expenses and increasing earnings). The concept typically applies to banks.
As of the end of Q2 2015, Facebook's Prineville data center had a power usage effectiveness (PUE) of 1.078 and its Forest City data center had a PUE of 1.082. [15] In October 2015, Allied Control has a claimed PUE ratio of 1.02 [16] through the use of two-phase immersion cooling using 3M Novec 7100 fluid.
Since operational efficiency is about the output to input ratio, it must be measured on both the input and output side. Quite often, company management is measuring primarily on the input side, e.g., the unit production cost or the man hours required to produce one unit.
A 1995 study of the cost-effectiveness of reviewed over 500 life-saving interventions found that the median cost-effectiveness was $42,000 per life-year saved. [7] A 2006 systematic review found that industry-funded studies often concluded with cost-effective ratios below $20,000 per QALY and low quality studies and those conducted outside the ...
Efficacy, efficiency, and effectivity are terms that can, in some cases, be interchangeable with the term effectiveness. The word effective is sometimes used in a quantitative way, "being very effective or not very effective". However, neither "effectiveness", nor "effectively", inform about the direction (positive or negative) or gives a ...