psyc 2017 CH9

psyc 2017 CH9 - Experimental Design Chapter9: Control...

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Chapter 9: Control Techniques Experimental Design Extraneous Variable
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Introduction Goal of experimentation--identify the causal effect of the IV Must have internal validity to do this Internal validity requires control of confounding variables Ways of achieving control Design of the experiment Statistical adjustments Incorporate control techniques into the research design
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Randomization A control technique to equate groups of participants. Only technique for controlling for unknown extraneous variables. Random selection —selecting people at random from a defined population. Random assignment —randomly assigning participants to treatment groups.
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Randomization Random Selection —selecting people at random from a defined population Insures that the sample selected is representative of the population. * Population Sample * O x * x * x O * O * x O * O x * O x
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Random Assignment —randomly assigning participants to treatment groups Randomly distributes the extraneous variables over the treatment groups. Randomization * Population Sample * O x * x * x O * O * x O * O x * O x * O x * O x Group 1 Group 2
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Randomization Procedures Random number tables Random number generators Excel Function - = RAND (). (no spaces) Drawing slips of paper from a hat Tossing a coin
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Matching Measuring Participants on various extraneous variables and then choosing other participants that score equally so that they are matched for the levels of the extraneous variables. Advantages of matching
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psyc 2017 CH9 - Experimental Design Chapter9: Control...

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