# Chapter 9: Control Techniques This multimedia product and its contents are protected under copyright law. The following are prohibited by law: Any public.

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Chapter 9: Control Techniques This multimedia product and its contents are protected under copyright law. The following are prohibited by law: Any public performance or display, including transmission of any image over a network; Preparation of any derivative work, including the extraction, in whole or in part, of any images; Any rental, lease, or lending of the program

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

Randomization This is the most important and basic control technique Random selectionselecting people at random from a defined population –Insures that the sample selected is representative of the population –Studies seldom if ever do this because of expense, etc

Random assignmentrandomly assigning participants to treatment groups –Provides maximum insurance that groups are equal –Equates groups because every person has an equal chance of being assigned to each group Accomplishes this by randomly distributing the extraneous variables over the treatment groups

Matching Use of any of a variety of techniques to equate participants in the treatment groups on specific variables Advantages of matching –Controls for the variables on which participants are matched –Increases the sensitivity of the experiment

Matching Techniques Holding variables constant –Disadvantages Restricts the population size Restricts generalization to the type of participants in the study Building the extraneous variable into the research design –Should be used only when you are interested in the of the extraneous variable

Matching by Equating Participants Matching by Equating Participants Precision controlmatch case by case –Disadvantages Identifying the variables on which to match Difficulty of matching participants increases as the number of variables on which to match increases Some variables difficult to match Frequency distribution controlmatch on the overall distribution of the selected var. –Disadvantage Combination of variables may be mismatched

Counterbalancing Used to control sequencing effects Type of sequencing effects –Carry-over effects –Order effects Counterbalancing procedures –Intrasubject or ABBA technique counterbalances on a case-by-case basis

Control of Participant Effects Double-blind Placebo Model Deception Control of participant interpretation –Retrospective verbal report –Concurrent verbal reports Sacrifice groups Concurrent probing Think-aloud technique

Control of Experimenter Effects Control of recording errors –use multiple data recorders –have participants make responses on a computer Control of attribute errors –use the same experimenter in all treatment conditions unless the treatment condition interacts with attribute

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