normal distribution - meaning and definition. What is normal distribution
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What (who) is normal distribution - definition

PROBABILITY DISTRIBUTION
Bell Curve; Gaussian distribution; NormalDistribution; Normal Distribution; Standard normal distribution; Law of error; Cumulative normal; Normally distributed; Cumulative Normal distribution; Normality (statistics); Standard normal; Normal density function; Normal curve; Normal distribution curve; Normal Curve; Normal random variable; The bell-shaped curve; Gaussian normal distribution; Gaussian Distributions; Gaussian Distribution; Bell-shaped; Gaussian random variable; Error Distribution; Bell-shaped curve; Standard distribution; Error distribution; Bell-curve; Normal distributions; Bell distribution; Normal probability distribution; Gaussian density; Gauss distribution; Normal cumulative distribution function; Bell Curves; Bell curves; Normal distribution about the mean; Gaussian probability density function; Gaussian probability distribution; Normal Model; Standard normal random variable; Gaussian profile; Normal-distribution; Bell-shaped frequency distribution curve; Gaussian distributions; Normal distribution quantile function; E-x2; E−x2; Normal population; Cumulative distribution function of the normal distribution; Bellcurve; Univariate Gaussian; Univariate Gaussian distribution; Bell curve; Bell shaped curve; Operations on normal deviates; Operations on normal distributions; Normal deviate; Standard normally distributed; Approximately normal distribution; Normalcdf; Gaussian pdf; Normal density; Normaldist
  • [[Carl Friedrich Gauss]] discovered the normal distribution in 1809 as a way to rationalize the [[method of least squares]].
  • As the number of discrete events increases, the function begins to resemble a normal distribution
  • Comparison of probability density functions, <math>p(k)</math> for the sum of <math>n</math> fair 6-sided dice to show their convergence to a normal distribution with increasing <math>na</math>, in accordance to the central limit theorem. In the bottom-right graph, smoothed profiles of the previous graphs are rescaled, superimposed and compared with a normal distribution (black curve).
  • Histogram of sepal widths for ''Iris versicolor'' from Fisher's [[Iris flower data set]], with superimposed best-fitting normal distribution.
  • Fitted cumulative normal distribution to October rainfalls, see [[distribution fitting]]
  •  [[Pierre-Simon Laplace]] proved the [[central limit theorem]] in 1810, consolidating the importance of the normal distribution in statistics.
  • The [[bean machine]], a device invented by [[Francis Galton]], can be called the first generator of normal random variables. This machine consists of a vertical board with interleaved rows of pins. Small balls are dropped from the top and then bounce randomly left or right as they hit the pins. The balls are collected into bins at the bottom and settle down into a pattern resembling the Gaussian curve.
  • '''a:''' Probability density of a function <math>\cos x^2</math> of a normal variable <math>x</math> with <math>\mu=-2</math> and <math>\sigma=3</math>. '''b:''' Probability density of a function <math>x^y</math> of two normal variables <math>x</math> and <math>y</math>, where <math>\mu_x=1</math>, <math>\mu_y=2</math>, <math>\sigma_x = 0.1</math>, <math>\sigma_y = 0.2</math>, and <math>\rho_{xy} = 0.8</math>. '''c:''' Heat map of the joint probability density of two functions of two correlated normal variables <math>x</math> and <math>y</math>, where <math>\mu_x = -2</math>, <math>\mu_y=5</math>, <math>\sigma_x^2 = 10</math>, <math>\sigma_y^2 = 20</math>, and <math>\rho_{xy} = 0.495</math>. '''d:''' Probability density of a function <math display="inline">\sum_{i=1}^4 \vert x_i \vert</math> of 4 iid standard normal variables. These are computed by the numerical method of ray-tracing.<ref name="Das" />
  • The ground state of a [[quantum harmonic oscillator]] has the [[Gaussian distribution]].
  • For the normal distribution, the values less than one standard deviation away from the mean account for 68.27% of the set; while two standard deviations from the mean account for 95.45%; and three standard deviations account for 99.73%.

normal distribution         
¦ noun Statistics a function that represents the distribution of many random variables as a symmetrical bell-shaped graph.
normal distribution         
<statistics> (Or "Gaussian distribution") The {frequency distribution} of many natural phenomena such as the height or intelligence of people of a certain age and sex. The formula looks something like: P(x) = e^(((x-m)/s)^2) where P(x) is the probability of a measurement x, m is the mean value of x and s is the standard deviation. Also known as a "bell curve" because of its shape. (2003-10-25)
Bell-shaped         
·adj Having the shape of a wide-mouthed bell; campanulate.

Wikipedia

Normal distribution

In statistics, a normal distribution or Gaussian distribution is a type of continuous probability distribution for a real-valued random variable. The general form of its probability density function is

f ( x ) = 1 σ 2 π e 1 2 ( x μ σ ) 2 {\displaystyle f(x)={\frac {1}{\sigma {\sqrt {2\pi }}}}e^{-{\frac {1}{2}}\left({\frac {x-\mu }{\sigma }}\right)^{2}}}

The parameter μ {\displaystyle \mu } is the mean or expectation of the distribution (and also its median and mode), while the parameter σ {\displaystyle \sigma } is its standard deviation. The variance of the distribution is σ 2 {\displaystyle \sigma ^{2}} . A random variable with a Gaussian distribution is said to be normally distributed, and is called a normal deviate.

Normal distributions are important in statistics and are often used in the natural and social sciences to represent real-valued random variables whose distributions are not known. Their importance is partly due to the central limit theorem. It states that, under some conditions, the average of many samples (observations) of a random variable with finite mean and variance is itself a random variable—whose distribution converges to a normal distribution as the number of samples increases. Therefore, physical quantities that are expected to be the sum of many independent processes, such as measurement errors, often have distributions that are nearly normal.

Moreover, Gaussian distributions have some unique properties that are valuable in analytic studies. For instance, any linear combination of a fixed collection of normal deviates is a normal deviate. Many results and methods, such as propagation of uncertainty and least squares parameter fitting, can be derived analytically in explicit form when the relevant variables are normally distributed.

A normal distribution is sometimes informally called a bell curve. However, many other distributions are bell-shaped (such as the Cauchy, Student's t, and logistic distributions). For other names, see Naming.

The univariate probability distribution is generalized for vectors in the multivariate normal distribution and for matrices in the matrix normal distribution.

Examples of use of normal distribution
1. Low–level officials do not grasp that hundreds of polling stations reporting figures in round numbers distort normal distribution, thus clearly revealing manipulations, Delyagin said.
2. He said it did not have the normal distribution of prions, the misfolded mad cow proteins that kill brain cells and leave spongy holes behind.
3. "That is within the normal distribution." In total, the company has 75 alliances, ranging from control at Genentech to minority participations and licensing agreements in small biotech businesses.
4. After that, it begins spiking on round numbers, indicating a much greater number of polling stations reporting a specific turnout than a normal distribution would predict.
5. A 30–year–old mother of two, Kadem is part of a novel Hindustan Lever initiative that enlists about 20,000 poor and mostly illiterate women to peddle such products as Lifebuoy soap and Pepsodent toothpaste in villages once considered too small, too destitute and too far from normal distribution channels to warrant attention.