CH 7

• Independent variable (IV)


  The variable (antecedent condition) an experimenter intentionally manipulates
• Levels of an independent variable


  The values of the IV created by the experimenter
• An experiment requires at least two levels of the independent variable
• Confounding


  When the value of an extraneous variable systematically changes along with the independent variable
• Dependent variable (DV)


  The outcome measure the experimenter uses to assess the change in behavior produced by the independent variable
• Operational definition


  Specifies the exact meaning of a variable in an experiment by defining it in terms of observable operations, procedures, and measurements
• Experimental operational definition (of the IV)


  Specifies the exact procedure for creating values of the independent variable
• Measured operational definition (of the DV)


  Specifies the exact procedure for measuring the dependent variable
• Nominal scale


  • Assigns items to two or more distinct categories that can be named using a shared feature, but does not measure their magnitude
• Ordinal scale


  • Measures the magnitude of the dependent variable using ranks, but does not assign precise values
• Interval scale


  • Measures the magnitude of the dependent variable using equal intervals between values with no absolute zero point
• Ratio scale


  • Measures the magnitude of the dependent variable using equal intervals between values and an absolute zero
• Reliability


  The consistency of experimental operational definitions and measured operational definitions
• Interrater reliability


  The degree to which observers agree in their measurement of the behavior
• Test-retest reliability


  The degree to which a person's scores are consistent across two or more administrations of a measurement procedure
• Interitem reliability


  Measures the degree to which different parts of an instrument (questionnaire or test) that are designed to measure the same variable achieve consistent results
• Validity


  The operational definition accurately manipulates the independent variable or measures the dependent variable
• Face validity


  The degree to which the validity of a manipulation or measurement technique is self-evident
• Content validity


  How accurately a measurement procedure samples the content of the dependent variable
• Predictive validity


  How accurately a measurement procedure predicts future performance
• Concurrent validity


  Compares scores on measuring instrument with an outside criterion
• Construct validity


  How accurately an operational definition represents a construct
• Internal validity


  The degree to which changes in the dependent variable across treatment conditions were due to the independent variable
• Confounding


  When an extraneous variable systematically changes across the experimental conditions
• History threat


  When an event outside the experiment threatens internal validity by changing the dependent variable
• Maturation threat


  When physical or psychological changes in the subject threaten internal validity by changing the dependent variable
• Testing threat


  When prior exposure to a measurement procedure affects performance on this measure during the experiment
• Instrumentation threat


  When changes in the measurement instrument or measuring procedure threatens internal validity
• Statistical regression threat


  When subjects are assigned to conditions on the basis of extreme scores, the measurement procedure is not completely reliable, and subjects are retested using the same procedure to measure change on the dependent variable
• Selection threat


  When individual differences are not balanced across treatment conditions by the assignment procedure
• Subject mortality threat


  When subjects drop out of experimental conditions at different rates
• Selection interactions


  When a selection threat combines with at least one other threat (history, maturation, statistical regression, subject mortality, or testing)
• Purpose of the Method section


  Describes the Participants, Apparatus or Materials, and Procedure of the experiment to provide the reader with sufficient detail to exactly replicate the study
• An Apparatus section is appropriate when the equipment used in a study was unique or specialized, or when we need to explain the capabilities of more common equipment