| Categorical variable | Data (variables) that differ only in kind, not in amount or degree.
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| Constant | A characteristic that has the same value for all individuals.
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| Dependent variable | A variable affected or expected to be affected by the independent variable; also called "criterion" or "outcome variable."
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| Directional hypothesis | A relational hypothesis stated in such a manner that a direction, often indicated by "greater than" or "less than," is hypothesized for the results.
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| Experimental variable | The variable that is manipulated (systematically altered) in an intervention study by the researcher.
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| Extraneous variable | A variable that makes possible an alternative explanation of results; an uncontrolled variable.
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| Hypothesis | A tentative, testable assertion regarding the occurrence of certain behaviors, phenomena, or events; a prediction of study outcomes.
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| Independent variable | A variable that affects (or is presumed to affect) the dependent variable under study and is included in the research design so that its effect can be determined; sometimes called the "experimental" or "treatment" variable.
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| Manipulated variable | See experimental variable.
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| Moderator variable | A variable that may or may not be controlled but has an effect on the research situation.
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| Nondirectional hypothesis | A prediction that a relationship exists without specifying its exact nature.
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| Outcome variable | See dependent variable.
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| Quantitative variable | A variable that varies in amount or degree, but not in kind.
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| Relationship | A connection between two qualities or characteristics (e.g., motivation and learning).
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| Treatment variable | see experimental variable.
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