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3.25.08 - MANIPULATION AND MEASUREMENT OF VARIABLES...

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MANIPULATION AND MEASUREMENT OF VARIABLES Operational Definitions of Concepts Problem: Many interesting concepts are too vague to work with. Concepts should be operationally defined by - thinking of them as variables; and - clearly saying how they are to be measured or manipulated. That is, they should be defined in terms of measurement operations, or in the case of independent variables, manipulation operations. Examples: IQ is an operational definition of intelligence; Taylor score is an operational definition of anxiety. Any operational definition gains precision but also narrows the meaning. In what follows, we’ll concentrate on measured variables. Measurement “To measure” means “To observe and record” values of a variable. Examples: Head circumference; Gas mileage; Birth rate Question: What makes a measurement “good”? Answer: A good measurement is reliable and valid. The General Measurement Model: Observed Value = True Value + Error The “Observed Value” is what we get from our measurement operation.
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