normal distribution

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1. the specific location or arrangement of continuing or successive objects or events in space or time.
2. the extent of a ramifying structure such as an artery or nerve and its branches.
3. the geographical range of an organism or disease.
frequency distribution in statistics, a mathematical function that describes the distribution of measurements on a scale for a specific population.
normal distribution a symmetrical distribution of scores with the majority concentrated around the mean; for example, that representing a large number of independent random events. It is in the shape of a bell-shaped curve. Called also gaussian distribution. See illustration.
 Normal distribution. The approximate percentage of the area (or frequency) lying under the curve between standard deviations is indicated. From Dorland's, 2000.
probability distribution a mathematical function that assigns to each measurable event in a sample group the probability that the event will occur.

nor·mal dis·tri·bu·tion

a specific bell-shaped frequency distribution commonly assumed by statisticians to represent the infinite population of measurements from which a sample has been drawn; characterized by two parameters, the mean (x) and the standard deviation (σ), in the equation:

normal distribution

(in statistics) a theoretic distribution frequency of variable data usually represented graphically by a bell-shaped curve that reaches a peak about the mean.

normal distribution

A bell-shaped frequency distribution of data, the plotted curve of which is symmetrical about the mean, indicating no significant deviation of the data set from the mean.

Properties of a normal distribution
Continuous and symmetrical, with both tails extending to infinity; arithmetic mean, mode, and median are identical. The curve’s shape is completely determined by the mean and standard deviation.

gaus·si·an dis·tri·bu·tion

(gow'sē-ăn dis'tri-byū'shŭn)
The statistical distribution of members of a population around the population mean. In a gaussian distribution, 68.2% of values fall within ± 1 standard deviation (SD); 95.4% fall within ± 2 SD of the mean; and 99.7% fall within ± 3 SD of the mean.
Synonym(s): bell-shaped curve, normal distribution.

normal distribution

Gaussian distribution, a distribution which when expressed graphically is bell-shaped. The distribution to which many frequency distributions of biological variables, such as height, weight, intelligence, etc correspond.


Johann K.F., German physicist, 1777-1855.
gauss - a unit of magnetic field intensity.
gaussian curve - a specific bell-shaped frequency distribution. Synonym(s): gaussian distribution; normal distribution
gaussian distribution - Synonym(s): gaussian curve

normal distribution

graphical distribution of normal data, following a bell-shaped curve; the mean, median and mode all coincide at the central high point of the curve; 67% of data lie within ± 1 standard deviation (sd) of the spread of the sample data; 95% lie within ± 2 sds

nor·mal dis·tri·bu·tion

(nōr'măl dis'tri-byū'shŭn)
Specific bell-shaped frequency distribution commonly assumed by statisticians to represent the infinite population of measurements from which a sample has been drawn.

normal distribution,

n a curve representing the frequency with which the values of a variable are obtained or observed when the number is infinite and variation is subject only to chance factors. The curve is a symmetrical, bell-shaped curve with the highest frequency occurring in the middle and gradually tapering toward the extremes. In a normal distribution, 68.2% of all scores cluster around the mean within approximately 1 standard deviation, 95.4% within approximately 2 standard deviations, and 99.7% within approximately 3 standard deviations. Also called
normal curve, Gauss' curve.


the arrangement of numerical data. The arrangement may be in accordance with magnitude, a frequency distribution, or in relation to geographical location, a spatial distribution.

age distribution
see age distribution.
bimodal distribution
the distribution has two regions of high frequency of observations separated by a zone of low frequency.
binomial distribution
a probability distribution associated with two mutually exclusive outcomes.
cluster distribution
a nonrandom distribution with observations aggregating about geographic or temporal variables. May be deceptive and merely reflect the distribution of an uneven population.
frequency distribution
a table or graph of the frequency of occurrence of each value of a variable.
Gaussian distribution
see normal distribution (below).
hypergeometric distribution
may apply to sampling without replacement of a finite population.
lognormal distribution
a distribution which is normal when the log values of the variable are considered.
normal distribution
a graph of the distribution appears as a bell-shaped curve which is symmetrical on the two sides of the vertical axis through the peak of the curve. Called also gaussian distribution.
parent distribution
the distribution (population) that was originally sampled.
Poisson distribution
regular distribution
distributed at regular intervals of time or space; all values within its given interval are equally likely.
sex distribution
an increase in frequency in one sex, which includes neutered males and neutered females. Called also sex-linked or sex-associated.
skewed distribution
a distribution in which the curve illustrating it is not symmetrical but has a long tail on one or other side of the graph.
spatial distribution
variations in distribution related to position in space, e.g. close to the door of a barn.
see t-test.
temporal distribution
variation in distribution related to time, e.g. occurrence of disease incidents after visits by veterinarians, inseminators, feed salesmen.


1. agreeing with the regular and established type. When said of a solution, it denotes one containing one chemical equivalent of solute per liter of solution; e.g. a 0.5 normal (0.5 N) solution has a concentration of 0.5 Eq/l. The use of standard units (Eq/l) is now generally preferred in pharmacy and clinical medicine although elsewhere molarity (M) is used.
2. in the context of infectious diseases, not immunized or infected.
3. statistically speaking, the values of a variable which follow a bell-shaped or Gaussian distribution.

normal distribution
see normal distribution.
normal limits
limits of the classification of 'normal' in the results of a test.
normal saline
contains 0.9% sodium chloride. Called also isotonic saline.
References in periodicals archive ?
In particular, the normalised area random variables converge to the standard normal distribution.
When X random variables has standard normal distribution, its probability density function, is to be as follows:
This value is obtained from the [cumulative] standard normal distribution table.
The two-piece normal distribution is a convenient way of representing departures from the symmetry of the normal distribution since probability calculations can still be based on the published tables of the standard normal distribution.
where |Phi~(x) is the standard normal distribution function, and
Let [PHI] (*) denote the standard normal distribution function.

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