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Accuracy and precision

In measurement of a set, accuracy refers to closeness of the measurements to a specific value, while precision refers to the closeness of the measurements to each other. Accuracy has two definitions: More it is a description of systematic errors, a measure of statistical bias. ISO calls this trueness. Alternatively, ISO defines accuracy as describing a combination of both types of observational error above, so high accuracy requires both high precision and high trueness. Precision is a description of a measure of statistical variability. In simpler terms, given a set of data points from repeated measurements of the same quantity, the set can be said to be accurate if their average is close to the true value of the quantity being measured, while the set can be said to be precise if the values are close to each other. In the first, more common definition of "accuracy" above, the two concepts are independent of each other, so a particular set of data can be said to be either accurate, or precise, or both, or neither.

In the fields of science and engineering, the accuracy of a measurement system is the degree of closeness of measurements of a quantity to that quantity's true value. The precision of a measurement system, related to reproducibility and repeatability, is the degree to which repeated measurements under unchanged conditions show the same results. Although the two words precision and accuracy can be synonymous in colloquial use, they are deliberately contrasted in the context of the scientific method; the field of statistics, where the interpretation of measurements plays a central role, prefers to use the terms bias and variability instead of accuracy and precision: bias is the amount of inaccuracy and variability is the amount of imprecision. A measurement system can be not precise, precise but not accurate, neither, or both. For example, if an experiment contains a systematic error increasing the sample size increases precision but does not improve accuracy; the result would be a inaccurate string of results from the flawed experiment.

Eliminating the systematic error improves accuracy but does not change precision. A measurement system is considered valid if it is both precise. Related terms include error; the terminology is applied to indirect measurements—that is, values obtained by a computational procedure from observed data. In addition to accuracy and precision, measurements may have a measurement resolution, the smallest change in the underlying physical quantity that produces a response in the measurement. In numerical analysis, accuracy is the nearness of a calculation to the true value. In military terms, accuracy refers to the accuracy of fire, the precision of fire expressed by the closeness of a grouping of shots at and around the centre of the target. In industrial instrumentation, accuracy is the measurement tolerance, or transmission of the instrument and defines the limits of the errors made when the instrument is used in normal operating conditions. Ideally a measurement device is both accurate and precise, with measurements all close to and clustered around the true value.

The accuracy and precision of a measurement process is established by measuring some traceable reference standard. Such standards are defined in the International System of Units and maintained by national standards organizations such as the National Institute of Standards and Technology in the United States; this applies when measurements are repeated and averaged. In that case, the term standard error is properly applied: the precision of the average is equal to the known standard deviation of the process divided by the square root of the number of measurements averaged. Further, the central limit theorem shows that the probability distribution of the averaged measurements will be closer to a normal distribution than that of individual measurements. With regard to accuracy we can distinguish: the difference between the mean of the measurements and the reference value, the bias. Establishing and correcting for bias is necessary for calibration; the combined effect of that and precision. A common convention in science and engineering is to express accuracy and/or precision implicitly by means of significant figures.

Here, when not explicitly stated, the margin of error is understood to be one-half the value of the last significant place. For instance, a recording of 843.6 m, or 843.0 m, or 800.0 m would imply a margin of 0.05 m, while a recording of 8436 m would imply a margin of error of 0.5 m. A reading of 8,000 m, with trailing zeroes and no decimal point, is ambiguous. To avoid this ambiguity, the number could be represented in scientific notation: 8.0 × 103 m indicates that the first zero is significant while 8.000 × 103 m indicates that all three zeroes are significant, giving a margin of 0.5 m. It is possible to use a multiple of the basic measurement unit: 8.0 km is equivalent to 8.0 × 103 m. In fact, it indicates a margin of 0.05 km. However, reliance on this convention can lead to false precision errors when accepting data from sources that do not obey it. For example, a source reporting a number like 153,753 with pre

Steve Smith (cricketer, born 1961)

Steven Barry Smith is a former Australian and New South Wales cricketer. He played in three Test matches and 28 One Day Internationals between 1983 and 1985, taking part in tours of Sri Lanka, the West Indies, India, he joined the Australian rebel tours to South Africa in 1985–86 and 1986–87. He was named one of South Africa's Cricketers of the Year. Steve Smith made his first grade debut for Bankstown when he was 17, his mother's cousin was test batsman Norm O'Neill, but he claimed a greater influence on his game was his father, a grade cricketer. He says a crucial stage in his development as a batsman moved to opener. Scores of 162 and 215 at the beginning of the 1981–82 season saw him make his first class debut for New South Wales that summer, he made 35 on his first class debut and he ended up getting 245 runs at an average of 40. Smith's good form continued the following season, making a top score of 263 in the Sheffield Shield, including 117 in a session, he was selected in Australia's one day side and scored 117 off 130 balls in only his third game, against New Zealand.

These efforts led to him being picked in the Australian squad to tour Sri Lanka in 1983. Smith scored throughout the 1983–84 domestic season, making 480 first class runs at an average of 43.63. He established himself as an excellent one day international batsman, scoring 106 against Pakistan and making two half centuries against the West Indies, he was picked to tour the West Indies in early 1984. There was some doubt he would be able to go after dislocating his shoulder during the one day finals but he recovered in time. Smith started the tour of the West Indies brilliantly, scoring a century in each innings in his first match, a draw against Guyana – the first time that feat had been accomplished in that country in ten years, he followed this up with 60 in the 1st one day international. Smith's good form with the bat, along with Roger Woolley's poor work behind the stumps in tour games, prompted the selectors to pick Smith as opener and move Wayne B. Phillips down the order and play him as wicketkeeper.

Smith's first test was not a memorable one for him – he scored 3 and 12, was dismissed twice by Joel Garner. However he followed this with a useful knock of 27, batting at number three, which helped set up an Australian victory in the 2nd ODI, he was meant to play in the second test, but fell ill and was replaced at the last minute by Dean Jones. Smith recovered in time for the next tour game, against Barbados, hit 66 in the second innings, he was failed twice again, getting out both times to Malcolm Marshall. He was dropped for the 4th test hit a vein of form, scoring a century against the Windward Islands, 84 against Jamaica, 50 in a one day international. Smith was recalled to the test team for the final test, he was injured so unable to bat in the second. Smith toured India in 1984, scoring a half century and impressing Sunil Gavaskar with the quality of his fielding, he played several one day games for Australia over the 1984–85 season, making three half centuries, was only let go from the team due to injury.

However he was unable to work his way back into the test team, failing to score a first class century all summer. Smith had been approached by Graham Yallop during the India tour to see if he was interested in touring South Africa with an unofficial Australian XI. After he missed selection in the Australian sides to tour Sharjah or England in early 1985, Smith asked to be considered for the team going to South Africa, he signed to play for two seasons, 1985–86 and 1986–87. When the news of the tour broke, tour organiser Bruce Francis claims Smith was one of several players Kerry Packer wanted to buy back into official Australian cricket, along with Dirk Wellham, Wayne B. Phillips and Graeme Wood. Packer succeeded in persuading those three not to go to South Africa, but not Smith. Francis said he thought Smith wanted to go on the tour for the money – $200,000 after tax – but because it gave him the chance to show he was not a one-day specialist. During the first South African tour Smith only played one "test", due to injury, but made the most of it, scoring a century in the first innings.

He made two half centuries in the one day internationals. During the second tour, Smith scored centuries in the 4th unofficial test matches, he scored more first class runs on that trip than any other Australian batsman. Smith returned to Australia for two seasons but was unable to recapture his previous form, with a highest first class score of 84 over two summers, he moved to South Africa and played for Transvaal for two seasons retired from first class cricket. Smith ran an indoor cricket centre, became a batting coach for Bankstown as well as a New South Wales selector. Francis, Bruce. Guilty? Bob Hawke or Kim Hughes?. ISBN 9780731653881. Steve Smith at ESPNcricinfo


Irolita is a genus of softnose skates in the family Arhynchobatidae known as round skates. There are two species, both endemic to Australia, found over soft bottoms on the outer continental shelves and upper continental slopes, at depths of 50–200 m for the southern round skate and 142–209 m for the western round skate; the distributions of the two species do not overlap. Irolita waitii McCulloch, 1911 Irolita westraliensis Last & Gledhill, 2008 Both species are unique amongst Australian skates in having a smooth circular heart-shaped pectoral fin disc; the head is short, with a small fleshy process at the tip of the snout and large spiracles behind the eyes. The nasal flaps are merged into a bilobed nasal curtain forward of the mouth; the jaws are arched with the upper teeth exposed. The teeth are sexually dimorphic; the pelvic fins are incised, with the anterior lobe moderately long and slender and the posterior lobe broadly rounded. The tail is narrow, tapering to a slender tip and bearing two small dorsal fins near the end.

The caudal fin is reduced to minute lobes. Males have alar thorns near the pectoral fin tips and the tail is covered with irregular rows of small recurved thorns

Shadow and Light

Shadow and Light is a 1951 French psychological drama film directed by Henri Calef and starring Simone Signoret, María Casares and Jean Marchat. The film's sets were designed by Rino Mondellini. Simone Signoret as Isabelle Leritz María Casares as Caroline Bessier Jean Marchat as Schurmann Pierre Dux as Docteur Gennari Albert Plantier as Eugène Germaine Reuver as La patronne Albert Michel as Le patron Jacques Berthier as Jacques Barroy René Berthier as Petit rôle Gérard Buhr as Le garçon de café Gérard Gervais as Petit rôle Yannick Muller Paul Villé as Le patron du restaurant Hayward, Susan. Simone Signoret: The Star as Cultural Sign. Continuum, 2004. Shadow and Light on IMDb


Trichomyrmex is a genus of ants in the subfamily Myrmicinae. Described by Mayr in 1865, it was raised as a genus in 2015; these ants are endemic to multiple continents. Trichomyrmex aberrans Forel, 1902 Trichomyrmex abyssinicus Trichomyrmex chobauti Trichomyrmex criniceps Trichomyrmex destructor Trichomyrmex emeryi Mayr, 1895 Trichomyrmex epinotale Santschi, 1923 Trichomyrmex glaber Trichomyrmex lameerei Trichomyrmex mayri Trichomyrmex muticus Trichomyrmex oscaris Forel, 1894 Trichomyrmex perplexus Trichomyrmex robustior Trichomyrmex rogeri Mayr, 1865 Trichomyrmex santschii Trichomyrmex scabriceps Trichomyrmex wroughtoni Forel, 1911

David Hugh Mellor

David Hugh Mellor is a British philosopher. He is a former Professor of Philosophy and Pro-Vice-Chancellor, now Professor Emeritus, of Cambridge University. Mellor was born in London on 10 July 1938, educated at Manchester Grammar School, he studied chemical engineering at Cambridge. His first formal study of philosophy was at the University of Minnesota where he took a minor in Philosophy of Science under Herbert Feigl. From Minnesota he obtained an MSc in 1962, he obtained his PhD in philosophy, with a thesis written under the supervision of Mary Hesse, at Penbroke in 1968. His primary work is metaphysics, although his philosophical interests include philosophy of science, philosophy of mind, probability and causation, laws of nature and properties, decision theory. Mellor was Professor of Philosophy at the University of Cambridge and Fellow of Darwin College from 1971 to 2005; as a professor he was the subject of extensive media coverage as the main opponent of the conferment of an honorary degree in philosophy to the French philosopher Jacques Derrida.

He was president of the Aristotelian Society from 1992 to 1993, a member of the Humanist Philosophers' Group of the British Humanist Association and Honorary Fellow of the Australian Academy of the Humanities. He was a Fellow of the British Academy between 1983 and 2008. In retirement Mellor now holds the title of Emeritus Professor, his Festschrift, Real Metaphysics, was published in 2003. Mellor is an amateur theatre actor; the Matter of Chance. Cambridge University Press. Real Time. Cambridge University Press. Real Time II. Routledge. Matters of Metaphysics. Cambridge University Press; the Facts of Causation. Routledge. Probability: A Philosophical Introduction. Routledge. Mind and Reality. Oxford University PressFor a more complete list of publications and works see Mellor's homepage and entry at PhilPapers. Real Metaphysics: Essays in Honour of D. H. Mellor. Hallvard Lillehammer and Gonzalo Rodriguez-Pereyra ed. Interviews with Philosophy Bites: Hugh Mellor on Time Hugh Mellor on Frank Ramsey on Truth Hugh Mellor on Probability Better Than The Stars 1978 BBC Radio programme made by Mellor about Frank Ramsey.

And "Cambridge Philosophers I: F. P. Ramsey" text of an article derived from the 1978 radio programme "An Interview with Hugh Mellor" Archived versions of Mellor's homepage and Faculty page