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The mean of a probability distributionis the long-run arithmetic average value of a random variablehaving that distribution. If the random variable is denoted by X{\displaystyle X}, then the mean is also known as the expected valueof X{\displaystyle X}(denoted E(X){\displaystyle E(X)}).
Definition. The arithmetic mean of a set of observed data is equal to the sum of the numerical values of each observation, divided by the total number of observations. Symbolically, for a data set consisting of the values , the arithmetic mean is defined by the formula: [ 2] (For an explanation of the summation operator, see summation .)
The weighted arithmetic mean is similar to an ordinary arithmetic mean (the most common type of average ), except that instead of each of the data points contributing equally to the final average, some data points contribute more than others. The notion of weighted mean plays a role in descriptive statistics and also occurs in a more general ...
The geometric mean can be understood in terms of geometry. The geometric mean of two numbers, and , is the length of one side of a square whose area is equal to the area of a rectangle with sides of lengths and . Similarly, the geometric mean of three numbers, , , and , is the length of one edge of a cube whose volume is the same as that of a ...
The harmonic mean ( H ) of the lognormal distribution of a random variable X is [ 17] where μ and σ2 are the parameters of the distribution, i.e. the mean and variance of the distribution of the natural logarithm of X . The harmonic and arithmetic means of the distribution are related by.
The first use of an equals sign, equivalent to 14 x + 15 = 71 in modern notation. From The Whetstone of Witte by Robert Recorde of Wales (1557). [ 1] In mathematics, an equation is a mathematical formula that expresses the equality of two expressions, by connecting them with the equals sign =. [ 2][ 3] The word equation and its cognates in ...
This approximate formula is for moderate to large sample sizes; the reference gives the exact formulas for any sample size, and can be applied to heavily autocorrelated time series like Wall Street stock quotes. Moreover, this formula works for positive and negative ρ alike. [12] See also unbiased estimation of standard deviation for more ...
Mean square. In mathematics and its applications, the mean square is normally defined as the arithmetic mean of the squares of a set of numbers or of a random variable. [1] It may also be defined as the arithmetic mean of the squares of the deviations between a set of numbers and a reference value (e.g., may be a mean or an assumed mean of the ...