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## alternative forms

In psychometrics, two or more similar versions of a psychometric test. If they are similar in content but have not been shown to have similar psychometric properties, then they are also called ...

## Berry–Esséen theorem

A theorem published in 1941 that concerns the distribution of the mean, X̄, of n independent identically distributed random variables, X1, X2,…, Xn. The theorem requires that the expected values of ...

## biserial correlation

A measure of the association between a binary variable, X, taking values 0 and 1, and a continuous random variable, Y. If it is assumed that for each value of X the distribution of Y is normal, with ...

## capability analysis

Method determining the extent to which the long-term performance of an industrial process complies with engineering requirements or managerial goals. Often it is required that output should lie ...

## Cauchy distribution

A continuous random variable with probability density function f given by , where k>0 and m are parameters, is said to have a Cauchy distribution.The graph of f is a bell-curve centred on m. The mode ...

## central tendency

In descriptive statistics, the middle or typical value of any probability distribution or set of scores, usually measured by the arithmetic mean, median, or mode.

## Chebyshev inequality

For a random variable X with expected value μ and standard deviation σ, for all positive values of the constant k. See also Bernstein inequality; Hölder inequality; Kolmogorov inequality; Markov ...

## coefficient of variation

A measure of variability within a sample, representing a population or a species; it is calculated as the standard deviation × 100 divided by the mean. Experience shows that within a homogenous ...

## Cohen's d

A measure of effect size, the most familiar form being the difference between two means (M1 and M2) expressed in units of standard deviations: the formula is d = (M1 − M2)/σ, where σ is the pooled ...

## control chart

A graphical representation of the statistically derived performance limits (normally ±2 standard deviations), which is used in statistical process control. By recording samples on a control chart, it ...

## correlation

A statistical measure of the relationship between two variables. It is the covariance of the variables divided by the product of their standard deviations.

## Cox–Mantel test

A non-parametric test for comparing two survival curves, which results from the work of Sir David Cox and Nathan Mantel. Denote the total number of deaths in the second group by D2, and let the ...

## d prime

In signal detection theory, an index of the detectability or discriminability of a signal, given by the difference between the means (or separation between the peaks) of the signal-plus-noise and the ...

## descriptive statistics

(dis-kript-iv)the use of statistics to organize and present data in a study in an informative way that describes the basic features of the data and enables analysis.

## deviation

N.(in marine insurance) The departure of a ship from an agreed course. A ship must follow the course specified in a voyage or mixed insurance policy (see time policy); if no course is specified, the ...

## deviation IQ

The modern, statistical conception of IQ, introduced in 1939 by the Romanian-born US psychologist David Wechsler (1896–1981), according to which IQ is a normally distributed variable with a mean of ...

## deviation score

In statistics, a score representing the difference between the raw score and the arithmetic mean of the raw scores in the group to which it belongs. For example, in the group of raw scores 1, 4, 10, ...

## dispersion

In descriptive statistics, the degree of scatter or variability in a group of scores, usually measured by the variance or standard deviation. See also interquartile range, probable error, range, ...

## error bar

On a graph of points representing means, a line through a point indicating the margin of error (see illustration). Error bars on a line graph or histogram may indicate confidence intervals, standard ...

## expected volatility

An estimate of the future standard deviation of the value of a particular financial variable. It is important in the valuation of options, since the higher the volatility of the security or commodity ...