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61-421: Mean is a term used in mathematics and statistics. Mean may also refer to: Mean The arithmetic mean , also known as "arithmetic average", is the sum of the values divided by the number of values. The arithmetic mean of a set of numbers x 1 , x 2 , ..., x n is typically denoted using an overhead bar , x ¯ {\displaystyle {\bar {x}}} . If

122-425: A color wheel —there is no mean to the set of all colors. In these situations, you must decide which mean is most useful. You can do this by adjusting the values before averaging, or by using a specialized approach for the mean of circular quantities . The Fréchet mean gives a manner for determining the "center" of a mass distribution on a surface or, more generally, Riemannian manifold . Unlike many other means,

183-421: A probability distribution is the long-run arithmetic average value of a random variable having that distribution. If the random variable is denoted by X {\displaystyle X} , then the mean is also known as the expected value of X {\displaystyle X} (denoted E ( X ) {\displaystyle E(X)} ). For a discrete probability distribution ,

244-445: A right triangle with legs a and b and altitude h from the hypotenuse to the right angle, h is half the harmonic mean of a and b . Let t and s ( t > s ) be the sides of the two inscribed squares in a right triangle with hypotenuse c . Then s equals half the harmonic mean of c and t . Let a trapezoid have vertices A, B, C, and D in sequence and have parallel sides AB and CD. Let E be

305-400: A truncated mean . It involves discarding given parts of the data at the top or the bottom end, typically an equal amount at each end and then taking the arithmetic mean of the remaining data. The number of values removed is indicated as a percentage of the total number of values. The interquartile mean is a specific example of a truncated mean. It is simply the arithmetic mean after removing

366-417: A function f ( x ) {\displaystyle f(x)} . Intuitively, a mean of a function can be thought of as calculating the area under a section of a curve, and then dividing by the length of that section. This can be done crudely by counting squares on graph paper, or more precisely by integration . The integration formula is written as: In this case, care must be taken to make sure that

427-399: A list of numbers, is the sum of all of the numbers divided by their count. Similarly, the mean of a sample x 1 , x 2 , … , x n {\displaystyle x_{1},x_{2},\ldots ,x_{n}} , usually denoted by x ¯ {\displaystyle {\bar {x}}} , is the sum of the sampled values divided by

488-421: A measure of central tendency ). The mean of a set of observations is the arithmetic average of the values; however, for skewed distributions , the mean is not necessarily the same as the middle value (median), or the most likely value (mode). For example, mean income is typically skewed upwards by a small number of people with very large incomes, so that the majority have an income lower than the mean. By contrast,

549-402: A range of cars one measure will produce the harmonic mean of the other – i.e., converting the mean value of fuel economy expressed in litres per 100 km to miles per gallon will produce the harmonic mean of the fuel economy expressed in miles per gallon. For calculating the average fuel consumption of a fleet of vehicles from the individual fuel consumptions, the harmonic mean should be used if

610-429: A roundtrip journey (see above). In any triangle , the radius of the incircle is one-third of the harmonic mean of the altitudes . For any point P on the minor arc BC of the circumcircle of an equilateral triangle ABC, with distances q and t from B and C respectively, and with the intersection of PA and BC being at a distance y from point P, we have that y is half the harmonic mean of q and t . In

671-414: A set of non-identical numbers is subjected to a mean-preserving spread — that is, two or more elements of the set are "spread apart" from each other while leaving the arithmetic mean unchanged — then the harmonic mean always decreases. For the special case of just two numbers, x 1 {\displaystyle x_{1}} and x 2 {\displaystyle x_{2}} ,

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732-444: A speed y , then its average speed is the arithmetic mean of x and y , which in the above example is 40 km/h. Average speed for the entire journey = ⁠ Total distance traveled / Sum of time for each segment ⁠ = ⁠ xt+yt / 2t ⁠ = ⁠ x+y / 2 ⁠ The same principle applies to more than two segments: given a series of sub-trips at different speeds, if each sub-trip covers

793-416: A wall at height A and the other leaning against the opposite wall at height B , as shown. The ladders cross at a height of h above the alley floor. Then h is half the harmonic mean of A and B . This result still holds if the walls are slanted but still parallel and the "heights" A , B , and h are measured as distances from the floor along lines parallel to the walls. This can be proved easily using

854-460: A weighted arithmetic mean, high data points are given greater weights than low data points. The weighted harmonic mean, on the other hand, correctly weights each data point. The simple weighted arithmetic mean when applied to non-price normalized ratios such as the P/E is biased upwards and cannot be numerically justified, since it is based on equalized earnings; just as vehicles speeds cannot be averaged for

915-485: A wide range of other notions of mean are often used in geometry and mathematical analysis ; examples are given below. In mathematics, the three classical Pythagorean means are the arithmetic mean (AM), the geometric mean (GM), and the harmonic mean (HM). These means were studied with proportions by Pythagoreans and later generations of Greek mathematicians because of their importance in geometry and music. The arithmetic mean (or simply mean or average ) of

976-467: Is a Schur-concave function, and is greater than or equal to the minimum of its arguments: for positive arguments, min ( x 1 … x n ) ≤ H ( x 1 … x n ) ≤ n min ( x 1 … x n ) {\displaystyle \min(x_{1}\ldots x_{n})\leq H(x_{1}\ldots x_{n})\leq n\min(x_{1}\ldots x_{n})} . Thus,

1037-486: Is an average which is useful for sets of numbers which are defined in relation to some unit , as in the case of speed (i.e., distance per unit of time): For example, the harmonic mean of the five values: 4, 36, 45, 50, 75 is If we have five pumps that can empty a tank of a certain size in respectively 4, 36, 45, 50, and 75 minutes, then the harmonic mean of 15 {\displaystyle 15} tells us that these five different pumps working together will pump at

1098-418: Is equal to 2.4 hours, to drain the pool together. This is one-half of the harmonic mean of 6 and 4: ⁠ 2·6·4 / 6 + 4 ⁠ = 4.8 . That is, the appropriate average for the two types of pump is the harmonic mean, and with one pair of pumps (two pumps), it takes half this harmonic mean time, while with two pairs of pumps (four pumps) it would take a quarter of this harmonic mean time. In hydrology ,

1159-438: Is equivalent to two thin lenses of focal length f hm , their harmonic mean, in series. Expressed as optical power , two thin lenses of optical powers P 1 and P 2 in series is equivalent to two thin lenses of optical power P am , their arithmetic mean, in series. The weighted harmonic mean is the preferable method for averaging multiples, such as the price–earnings ratio (P/E). If these ratios are averaged using

1220-447: Is found, invert it so as to find the "true" average trip speed. For each trip segment i, the slowness s i = 1/speed i . Then take the weighted arithmetic mean of the s i 's weighted by their respective distances (optionally with the weights normalized so they sum to 1 by dividing them by trip length). This gives the true average slowness (in time per kilometre). It turns out that this procedure, which can be done with no knowledge of

1281-423: Is related to the other Pythagorean means, as seen in the equation below. This can be seen by interpreting the denominator to be the arithmetic mean of the product of numbers n times but each time omitting the j -th term. That is, for the first term, we multiply all n numbers except the first; for the second, we multiply all n numbers except the second; and so on. The numerator, excluding the n , which goes with

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1342-487: Is the probability density function . In all cases, including those in which the distribution is neither discrete nor continuous, the mean is the Lebesgue integral of the random variable with respect to its probability measure . The mean need not exist or be finite; for some probability distributions the mean is infinite ( +∞ or −∞ ), while for others the mean is undefined . The generalized mean , also known as

1403-840: The arithmetic mean is always the greatest of the three and the geometric mean is always in between. (If all values in a nonempty data set are equal, the three means are always equal.) It is the special case M −1 of the power mean : H ( x 1 , x 2 , … , x n ) = M − 1 ( x 1 , x 2 , … , x n ) = n x 1 − 1 + x 2 − 1 + ⋯ + x n − 1 {\displaystyle H\left(x_{1},x_{2},\ldots ,x_{n}\right)=M_{-1}\left(x_{1},x_{2},\ldots ,x_{n}\right)={\frac {n}{x_{1}^{-1}+x_{2}^{-1}+\cdots +x_{n}^{-1}}}} Since

1464-414: The gene pool limiting the genetic variation present in the population for many generations to come. When considering fuel economy in automobiles two measures are commonly used – miles per gallon (mpg), and litres per 100 km. As the dimensions of these quantities are the inverse of each other (one is distance per volume, the other volume per distance) when taking the mean value of the fuel economy of

1525-514: The harmonic mean is a kind of average , one of the Pythagorean means . It is the most appropriate average for ratios and rates such as speeds, and is normally only used for positive arguments. The harmonic mean is the reciprocal of the arithmetic mean of the reciprocals of the numbers, that is, the generalized f-mean with f ( x ) = 1 x {\displaystyle f(x)={\frac {1}{x}}} . For example,

1586-595: The inequality of arithmetic and geometric means , this shows for the n = 2 case that H ≤ G (a property that in fact holds for all n ). It also follows that G = A H {\displaystyle G={\sqrt {AH}}} , meaning the two numbers' geometric mean equals the geometric mean of their arithmetic and harmonic means. For the special case of three numbers, x 1 {\displaystyle x_{1}} , x 2 {\displaystyle x_{2}} and x 3 {\displaystyle x_{3}} ,

1647-476: The recall (true positives per real positive) is often used as an aggregated performance score for the evaluation of algorithms and systems: the F-score (or F-measure). This is used in information retrieval because only the positive class is of relevance , while number of negatives, in general, is large and unknown. It is thus a trade-off as to whether the correct positive predictions should be measured in relation to

1708-458: The weighted harmonic mean is defined by The unweighted harmonic mean can be regarded as the special case where all of the weights are equal. The prime number theorem states that the number of primes less than or equal to n {\displaystyle n} is asymptotically equal to the harmonic mean of the first n {\displaystyle n} natural numbers . In many situations involving rates and ratios ,

1769-501: The Fréchet mean is defined on a space whose elements cannot necessarily be added together or multiplied by scalars. It is sometimes also known as the Karcher mean (named after Hermann Karcher). In geometry, there are thousands of different definitions for the center of a triangle that can all be interpreted as the mean of a triangular set of points in the plane. This is an approximation to

1830-636: The alloy (exclusive of typically minor volume changes due to atom packing effects) is the weighted harmonic mean of the individual densities, weighted by mass, rather than the weighted arithmetic mean as one might at first expect. To use the weighted arithmetic mean, the densities would have to be weighted by volume. Applying dimensional analysis to the problem while labeling the mass units by element and making sure that only like element-masses cancel makes this clear. If one connects two electrical resistors in parallel, one having resistance x (e.g., 60  Ω ) and one having resistance y (e.g., 40 Ω), then

1891-438: The area formula of a trapezoid and area addition formula. In an ellipse , the semi-latus rectum (the distance from a focus to the ellipse along a line parallel to the minor axis) is the harmonic mean of the maximum and minimum distances of the ellipse from a focus. In computer science , specifically information retrieval and machine learning , the harmonic mean of the precision (true positives per predicted positive) and

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1952-1604: The arithmetic mean, is the geometric mean to the power  n . Thus the n -th harmonic mean is related to the n -th geometric and arithmetic means. The general formula is H ( x 1 , … , x n ) = ( G ( x 1 , … , x n ) ) n A ( x 2 x 3 ⋯ x n , x 1 x 3 ⋯ x n , … , x 1 x 2 ⋯ x n − 1 ) = ( G ( x 1 , … , x n ) ) n A ( 1 x 1 ∏ i = 1 n x i , 1 x 2 ∏ i = 1 n x i , … , 1 x n ∏ i = 1 n x i ) . {\displaystyle H\left(x_{1},\ldots ,x_{n}\right)={\frac {\left(G\left(x_{1},\ldots ,x_{n}\right)\right)^{n}}{A\left(x_{2}x_{3}\cdots x_{n},x_{1}x_{3}\cdots x_{n},\ldots ,x_{1}x_{2}\cdots x_{n-1}\right)}}={\frac {\left(G\left(x_{1},\ldots ,x_{n}\right)\right)^{n}}{A\left({\frac {1}{x_{1}}}{\prod \limits _{i=1}^{n}x_{i}},{\frac {1}{x_{2}}}{\prod \limits _{i=1}^{n}x_{i}},\ldots ,{\frac {1}{x_{n}}}{\prod \limits _{i=1}^{n}x_{i}}\right)}}.} If

2013-429: The duration of that portion, while for the harmonic mean, the corresponding weight is the distance. In both cases, the resulting formula reduces to dividing the total distance by the total time.) However, one may avoid the use of the harmonic mean for the case of "weighting by distance". Pose the problem as finding "slowness" of the trip where "slowness" (in hours per kilometre) is the inverse of speed. When trip slowness

2074-489: The effect is the same as if one had used two resistors with the same resistance, both equal to the harmonic mean of x and y (48 Ω): the equivalent resistance, in either case, is 24 Ω (one-half of the harmonic mean). This same principle applies to capacitors in series or to inductors in parallel. However, if one connects the resistors in series, then the average resistance is the arithmetic mean of x and y (50 Ω), with total resistance equal to twice this,

2135-410: The entire journey = ⁠ Total distance traveled / Sum of time for each segment ⁠ = ⁠ 2 d / ⁠ d / x ⁠ + ⁠ d / y ⁠ ⁠ = ⁠ 2 / ⁠ 1 / x ⁠ + ⁠ 1 / y ⁠ ⁠ However, if the vehicle travels for a certain amount of time at a speed x and then the same amount of time at

2196-501: The fleet uses miles per gallon, whereas the arithmetic mean should be used if the fleet uses litres per 100 km. In the USA the CAFE standards (the federal automobile fuel consumption standards) make use of the harmonic mean. In chemistry and nuclear physics the average mass per particle of a mixture consisting of different species (e.g., molecules or isotopes) is given by the harmonic mean of

2257-512: The harmonic mean can be written as: In this special case, the harmonic mean is related to the arithmetic mean A = x 1 + x 2 2 {\displaystyle A={\frac {x_{1}+x_{2}}{2}}} and the geometric mean G = x 1 x 2 , {\displaystyle G={\sqrt {x_{1}x_{2}}},} by Since G A ≤ 1 {\displaystyle {\tfrac {G}{A}}\leq 1} by

2318-538: The harmonic mean can be written as: Three positive numbers H , G , and A are respectively the harmonic, geometric, and arithmetic means of three positive numbers if and only if the following inequality holds If a set of weights w 1 {\displaystyle w_{1}} , ..., w n {\displaystyle w_{n}} is associated to the data set x 1 {\displaystyle x_{1}} , ..., x n {\displaystyle x_{n}} ,

2379-408: The harmonic mean cannot be made arbitrarily large by changing some values to bigger ones (while having at least one value unchanged). The harmonic mean is also concave for positive arguments, an even stronger property than Schur-concavity. For all positive data sets containing at least one pair of nonequal values , the harmonic mean is always the least of the three Pythagorean means, while

2440-489: The harmonic mean is similarly used to average hydraulic conductivity values for a flow that is perpendicular to layers (e.g., geologic or soil) - flow parallel to layers uses the arithmetic mean. This apparent difference in averaging is explained by the fact that hydrology uses conductivity, which is the inverse of resistivity. In sabermetrics , a baseball player's Power–speed number is the harmonic mean of their home run and stolen base totals. In population genetics ,

2501-411: The harmonic mean is used when calculating the effects of fluctuations in the census population size on the effective population size. The harmonic mean takes into account the fact that events such as population bottleneck increase the rate genetic drift and reduce the amount of genetic variation in the population. This is a result of the fact that following a bottleneck very few individuals contribute to

Mean (disambiguation) - Misplaced Pages Continue

2562-670: The harmonic mean of 1, 4, and 4 is The harmonic mean H of the positive real numbers x 1 , x 2 , … , x n {\displaystyle x_{1},x_{2},\ldots ,x_{n}} is It is the reciprocal of the arithmetic mean of the reciprocals, and vice versa: where the arithmetic mean is A ( x 1 , x 2 , … , x n ) = 1 n ∑ i = 1 n x i . {\textstyle A(x_{1},x_{2},\ldots ,x_{n})={\tfrac {1}{n}}\sum _{i=1}^{n}x_{i}.} The harmonic mean

2623-421: The harmonic mean of a list of numbers tends strongly toward the least elements of the list, it tends (compared to the arithmetic mean) to mitigate the impact of large outliers and aggravate the impact of small ones. The arithmetic mean is often mistakenly used in places calling for the harmonic mean. In the speed example below for instance, the arithmetic mean of 40 is incorrect, and too big. The harmonic mean

2684-462: The harmonic mean provides the correct average . For instance, if a vehicle travels a certain distance d outbound at a speed x (e.g. 60 km/h) and returns the same distance at a speed y (e.g. 20 km/h), then its average speed is the harmonic mean of x and y (30 km/h), not the arithmetic mean (40 km/h). The total travel time is the same as if it had traveled the whole distance at that average speed. This can be proven as follows: Average speed for

2745-402: The harmonic mean, amounts to the same mathematical operations as one would use in solving this problem by using the harmonic mean. Thus it illustrates why the harmonic mean works in this case. Similarly, if one wishes to estimate the density of an alloy given the densities of its constituent elements and their mass fractions (or, equivalently, percentages by mass), then the predicted density of

2806-443: The integral converges. But the mean may be finite even if the function itself tends to infinity at some points. Angles , times of day, and other cyclical quantities require modular arithmetic to add and otherwise combine numbers. In all these situations, there will not be a unique mean. For example, the times an hour before and after midnight are equidistant to both midnight and noon. It is also possible that no mean exists. Consider

2867-406: The intersection of the diagonals , and let F be on side DA and G be on side BC such that FEG is parallel to AB and CD. Then FG is the harmonic mean of AB and DC. (This is provable using similar triangles.) One application of this trapezoid result is in the crossed ladders problem , where two ladders lie oppositely across an alley, each with feet at the base of one sidewall, with one leaning against

2928-411: The lowest and the highest quarter of values. assuming the values have been ordered, so is simply a specific example of a weighted mean for a specific set of weights. In some circumstances, mathematicians may calculate a mean of an infinite (or even an uncountable ) set of values. This can happen when calculating the mean value y avg {\displaystyle y_{\text{avg}}} of

2989-422: The mean and size of sample i {\displaystyle i} respectively. In other applications, they represent a measure for the reliability of the influence upon the mean by the respective values. Sometimes, a set of numbers might contain outliers (i.e., data values which are much lower or much higher than the others). Often, outliers are erroneous data caused by artifacts . In this case, one can use

3050-423: The mean for a moderately skewed distribution. It is used in hydrocarbon exploration and is defined as: where P 10 {\textstyle P_{10}} , P 50 {\textstyle P_{50}} and P 90 {\textstyle P_{90}} are the 10th, 50th and 90th percentiles of the distribution, respectively. Harmonic mean In mathematics ,

3111-598: The mean is given by ∑ x P ( x ) {\displaystyle \textstyle \sum xP(x)} , where the sum is taken over all possible values of the random variable and P ( x ) {\displaystyle P(x)} is the probability mass function . For a continuous distribution , the mean is ∫ − ∞ ∞ x f ( x ) d x {\displaystyle \textstyle \int _{-\infty }^{\infty }xf(x)\,dx} , where f ( x ) {\displaystyle f(x)}

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3172-409: The median income is the level at which half the population is below and half is above. The mode income is the most likely income and favors the larger number of people with lower incomes. While the median and mode are often more intuitive measures for such skewed data, many skewed distributions are in fact best described by their mean, including the exponential and Poisson distributions. The mean of

3233-429: The number of items in the sample. For example, the arithmetic mean of five values: 4, 36, 45, 50, 75 is: The geometric mean is an average that is useful for sets of positive numbers, that are interpreted according to their product (as is the case with rates of growth) and not their sum (as is the case with the arithmetic mean): For example, the geometric mean of five values: 4, 36, 45, 50, 75 is: The harmonic mean

3294-476: The number of predicted positives or the number of real positives, so it is measured versus a putative number of positives that is an arithmetic mean of the two possible denominators. A consequence arises from basic algebra in problems where people or systems work together. As an example, if a gas-powered pump can drain a pool in 4 hours and a battery-powered pump can drain the same pool in 6 hours, then it will take both pumps ⁠ 6·4 / 6 + 4 ⁠ , which

3355-475: The numbers are from observing a sample of a larger group , the arithmetic mean is termed the sample mean ( x ¯ {\displaystyle {\bar {x}}} ) to distinguish it from the group mean (or expected value ) of the underlying distribution, denoted μ {\displaystyle \mu } or μ x {\displaystyle \mu _{x}} . Outside probability and statistics,

3416-517: The parameter m , the following types of means are obtained: This can be generalized further as the generalized f -mean and again a suitable choice of an invertible f will give The weighted arithmetic mean (or weighted average) is used if one wants to combine average values from different sized samples of the same population: Where x i ¯ {\displaystyle {\bar {x_{i}}}} and w i {\displaystyle w_{i}} are

3477-511: The power mean or Hölder mean, is an abstraction of the quadratic , arithmetic, geometric, and harmonic means. It is defined for a set of n positive numbers x i by x ¯ ( m ) = ( 1 n ∑ i = 1 n x i m ) 1 m {\displaystyle {\bar {x}}(m)=\left({\frac {1}{n}}\sum _{i=1}^{n}x_{i}^{m}\right)^{\frac {1}{m}}} By choosing different values for

3538-400: The same distance , then the average speed is the harmonic mean of all the sub-trip speeds; and if each sub-trip takes the same amount of time , then the average speed is the arithmetic mean of all the sub-trip speeds. (If neither is the case, then a weighted harmonic mean or weighted arithmetic mean is needed. For the arithmetic mean, the speed of each portion of the trip is weighted by

3599-407: The same rate as much as five pumps that can each empty the tank in 15 {\displaystyle 15} minutes. AM, GM, and HM satisfy these inequalities: Equality holds if all the elements of the given sample are equal. In descriptive statistics , the mean may be confused with the median , mode or mid-range , as any of these may incorrectly be called an "average" (more formally,

3660-422: The sum of x and y (100 Ω). This principle applies to capacitors in parallel or to inductors in series. As with the previous example, the same principle applies when more than two resistors, capacitors or inductors are connected, provided that all are in parallel or all are in series. The "conductivity effective mass" of a semiconductor is also defined as the harmonic mean of the effective masses along

3721-409: The three crystallographic directions. As for other optic equations , the thin lens equation ⁠ 1 / f ⁠ = ⁠ 1 / u ⁠ + ⁠ 1 / v ⁠ can be rewritten such that the focal length f is one-half of the harmonic mean of the distances of the subject u and object v from the lens. Two thin lenses of focal length f 1 and f 2 in series

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