# standard deviation

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Related to Standard deviations: variance, standard error

## deviation

[de″ve-a´shun]**1.**a turning away from the regular standard or course.

**2.**in ophthalmology, strabismus.

**3.**in statistics, the difference between a sample value and the mean.

**axis deviation**an axis shift in the frontal plane, as seen on an electrocardiogram. There are three types:

*Left,*from −30° to −90°;

*Right,*from +90° to +180°; and

*Undetermined,*which may be either extreme left or extreme right, from −90° to +180°.

**conjugate deviation**dysfunction of the ocular muscles causing the two eyes to diverge to the same side when at rest.

**sexual deviation**sexual behavior or fantasy outside that which is morally, biologically, or legally sanctioned, often specifically one of the paraphilias.

**standard deviation**(SD) the dispersion of a random variable; a measure of the amount by which each value deviates from the mean. It is equal to the square root of the variance. For data that have a normal distribution, about 68 per cent of the data points fall within (plus or minus) one standard deviation from the mean and about 95 per cent fall within (plus or minus) two standard deviations. Symbol σ.

**ulnar deviation**a hand deformity, seen in chronic rheumatoid arthritis and lupus erythematosus, in which swelling of the metacarpophalangeal joints causes the fingers to become displaced to the ulnar side. Called also ulnar drift. See illustration.

## stan·dard de·vi·a·tion (SD, σ),

**1.**statistical index of the degree of deviation from central tendency, namely, of the variability within a distribution; the square root of the average of the squared deviations from the mean.

**2.**a measure of dispersion or variation used to describe a characteristic of a frequency distribution.

## standard deviation

A statistical term that indicates the relative variability of a value around its mean; the square root of variance.## standard deviation

Square root of the variance Statistics The most widely used measure of the dispersion of a set of values about a mean, which is equal to the positive square root of the variance, where a graphic representation of the data points is described by a curve with Gaussian distribution–GD–ie, bell-shaped. See Gaussian curve.## stan·dard de·vi·a·tion

**(σ, SD)**(stan'dărd dē'vē-ā'shŭn)

**1.**Statistical index of the degree of deviation from central tendency, namely, of the variability within a distribution; the square root of the average of the squared deviations from the mean.

**2.**A measure of dispersion or variation used to describe a characteristic of a frequency distribution.

## standard deviation

A measure of dispersion widely used in statistics. Standard deviation is the square root of the arithmetic average of the squares of the deviations of the members of a sample from the mean.## standard deviation (S)

a measure of the variation in a sample, calculated as the square root of the VARIANCE. Mean values are often followed by the standard deviation.see STANDARD ERROR.## Standard deviation

A measure of the distribution of scores around the average (mean). In a normal distribution, two standard deviations above and below the mean includes about 95% of all samples.

Mentioned in: Stanford-Binet Intelligence Scales, Wechsler Intelligence Test

## stan·dard de·vi·a·tion

**(SD)**(stan'dărd dē'vē-ā'shŭn)

**1.**Statistical index of degree of deviation from central tendency, namely, of variability within a distribution; square root of average of squared deviations from mean.

**2.**Measure of dispersion or variation used to describe a characteristic of a frequency distribution.

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