# distribution

distribution (dis-tri-byu´shun)

1. The passage of the branches of arteries or nerves to the tissues and organs. 2. The area in which the branches of an artery or a nerve terminate, or the area supplied by such an artery or nerve. 3. The relative numbers of individuals in each of various categories or populations such as in different age, sex, or occupational samples. See frequency d. [L. dis-tribuo, pp. -tributus, to distribute, fr. tribus, a tribe]
Bernoulli d. the probability d. associated with two mutually exclusive and exhaustive outcomes, e.g., death or survival.
binomial d. 1. a probability d. associated with two mutually exclusive outcomes, e.g., presence or absence of a clinical sign. 2. the possible array of the number of successes in the outcomes from a fixed number, n, of independent Bernoulli trials; the probabilities associated with each constitute a binomial process of order n.
chi-square d. (kI) a variable is said to have a chi-square d. with K degrees of freedom if it is distributed like the sum of the squares of K independent random variables, each of which has a normal (gaussian) d. with mean zero and variance one. The chi square d. is the basis for many variations of the chi-square(d) test, perhaps the most widely used test for statistical significance in biology and medicine.
countercurrent d. a method of separation of two or more substances by repeated distribution between two immiscible liquid phases that move past each other in opposite directions; a form of liquid-liquid chromatography.
dermatomal d. dermatome (3)
epidemiological d. See histogram.
exponential d. the time until failure of a process at constant hazard.
f d. the d. of the ratio of two independent quantities each of which is distributed like a variance in normally distributed samples. So named in honor of the English statistician and geneticist R.A. Fisher.
frequency d. a statistical description of raw data in terms of the number or frequency of items characterized by each of a series or range of values of a continuous variable.
gaussian d. normal d
lognormal d. if a variable y is such that x = log y, it is said to have a lognormal d.; this is a skew d.
multinomial d. probability distribution associated with the classification of each of a sample of individuals into one of several mutually exclusive and exhaustive categories.
normal d. a specific bell-shaped frequency d. 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 (sigma), in the equation:gaussian curve, gaussian d;
Poisson d. 1. a discontinuous d. important in statistical work and defined by the equation p (x) = e -mumux/ x!, where e is the base of natural logarithms, x is the sequence of integers, mu is the mean, and x! represents the factorial of x. 2. a d. function used to describe the occurrence of rare events, or the sampling d. of isolated counts in a continuum of time or space.
skew d. an asymmetrical frequency d.; in biology and medicine it is usually a lognormal d.
t d. the d. of the quotient of independent random variables, the numerator of which is a standardized normal variate and the denominator the positive square root of the quotient of a chi-square distributed variate and its number of degrees of freedom.

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