# variable

variable (var´e-a-bl)

1. That which is inconstant, which can or does change, as contrasted with a constant. 2. Deviating from the type in structure, form, physiology, or behavior. [L. vario, to vary, change, differ]
continuous v. a v. that may take on any value in an interval or intervals (its domain).
continuous random v. continuous v. that may randomly assume any value in its domain but any particular value has no probability of occurring, only a probability density.
dependent v. in experiments, a v. that is influenced by or dependent upon changes in the independent v.; e.g., the amount of a written passage retained (dependent v.) as a function of the different numbers of minutes (independent v.) allowed to study the passage.
discrete v. a v. that may assume only a countable (usually finite) number of values.
discrete random v. a random v. that may assume a countable number of values, each with a probability strictly greater than zero.
independent v. a characteristic being measured or observed that is hypothesized to influence another event or manifestation (the dependent v.) within a defined area of relationships under study; that is, the independent v. is not influenced by the event or manifestation, but may cause it or contribute to its variation. See dependent v.
intermediate v. a v. in a causal pathway that causes variation in the dependent v. and is itself caused to vary by the independent v.
intervening v. an event, such as an attitude or emotion, inferred to occur within an organism between the stimulation and response in such a way as to influence or determine the response.
mixed discrete-continuous random v. a random v. that may assume some values with probabilities and others with probability densities. For example, in a 35-year-old man with familial polyposis of the colon, the distribution of time until malignant disease occurs consists of a probability that he already has cancer (which would be assigned the waiting time 0), a probability density of developing it in the future and a probability that he will die of some other cause before he develops cancer.
moderator v. a v. that interacts by virtue of being antecedent or intermediate in the causal pathway.
random v. a v. that may assume a set of values, each with fixed probabilities or probability densities (its distribution), in such a way that the total probability assigned to the distribution is unity; the random v. may be discrete, continuous, or mixed discrete-continuous.

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