| confounding | An uncontrolled variable varies systematically with an independent variable; it.is impossible to separate the effect of the independent variable from the confounding interval.
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| confounding variable | A variable that is not controlled in a research investigation. In an experiment, the experimental groups differ on both the independent variable and the confounding variable.
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| construct validity | The degree to which a measurement device accurately measures the theoretical construct it is designed to measure.
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| correlation coefficient | An index of how strongly two variables are related to each other.
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| curvilinear relationship | A relationship in which increases in the values of the first variable are accompanied by both increases and decreases in the values of the second variable.
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| dependent variable | The variable that is the subject's response to, and dependent on, the level of the manipulated independent variable.
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| experimental method | A method of determining whether variables are related in which the researcher manipulates the independent variable and controls all other variables either by randomization or by direct experimental control.
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| external validity | The degree to which the results of an experiment may be generalized.
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| field experiment | An experiment that is conducted in a natural setting rather than a laboratory setting.
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| independent variable | The variable that is manipulated to observe its effect on the dependent variable.
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| internal validity | The certainty with which results of an experiment can be attributed to the manipulation of the independent variable rather than to some other, confounding variable.
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| negative linear relationship | A relationship in which increases in the values of the first variable are accompanied by decreases in the values of the second variable.
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| nonexperimental method | Use of measurement of variables to determine whether variables are related to one another. Also called correlational method.
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| operational definition | Definition of a concept that specifies the operation used to measure or manipulate the concept.
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| positive linear relationship | A relationship in which increases in the values of the first variable are accompanied by increases in the values of the second variable.
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| randomization | Controlling for the effects of extraneous variables by ensuring that the variables operate in a manner determined entirely by chance.
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| variable | Any event, situation, behavior, or individual characteristic that varies-that is, has at least two values.
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