Variable/Independent variable/Dependent variable

Quantifiable characteristic which varies amongst the population with more than one value (height, gender, age, etc.);

also, that which is capable of changing or being changed; a quantity’s characteristic of taking or exhibiting different values.

in experimental science, a variable is selected and manipulated – the independent variable (also referred to as the suspected cause or causal factor or agent) – to determine whether systematic changes in it results in changes in another variable – the dependent variable (also called simply the effect) – that is, whether the value of the latter depends upon the former.

A set of variables may be exclusive in that a member of the population can only exhibit one value and exhaustive in that every member of the population must exhibit some (particular) value.

More generally, any condition or factor which is related to a particular outcome.

Continuous variable

Any variable which lies along a dimension, range, or spectrum, rather than in a discrete category – expressed in terms of quantity, magnitude, or degree.

Dichotomous variable

Any variable which can be placed into either of two discrete and mutually exclusive categories.

A hidden variable is any other variable or factor which could explain the outcome differences between the two (or more) groups in a study (see: sampling error)

(see also: Studies – Scientific or Empirical, variability, experimental research, cause, effect, control group, double-blind, experimenter bias, randomized assignment, confound/confounding, correlation)