Chapter 7 - Chapter 7 Control Techniques in Experimental...

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Chapter 7: Control Techniques in Experimental Research 1. Differential influence- when the influence of an extraneous variable is different for the various groups 2. Method of difference- if groups are equivalent on every variable except for one, then that one variable is the cause of the difference between the groups a. Created by John Stuart Mill 3. Strongest experimental designs include randomization 4. Control techniques started at beginning of experiment a. Randomization/random assignment- equates groups of participants by ensuring every member an equal chance of being assigned to any group b. Only technique for controlling both known and unknown sources of extraneous variation c. When the distributions of extraneous variables are approximately equal in all groups, the influence of extraneous variables is held constant because they cannot exert any differential influence on the DV d. Want groups to be equivalent on any and all extraneous variables 5. Matching a. When random assignment is not possible, matching is the next effective technique b. Using any of a variety of techniques for equating participants on one or more variables c. Strength- ensures that participants in the different groups are equated on the matching variables c.i. Matching variable- extraneous variable used in matching d. Weakness- groups are equated only on the matching variables e. Matching By Holding Variables Constant e.i. Control extraneous variable hold the extraneous variable constant for all groups in the experiment e.i.1. All participants in each treatment group will have the same degree or type of extraneous variable e.ii. Disadvantages- e.ii.1. Technique restricts the size of the participant population e.ii.2. Results of the study can be generalized only to the type of participant who participated in the study e.ii.2.a. Study only conducted with females, can’t be generalized to males as well f. Matching by Building the Extraneous Variable into the Research Design f.i. Sometimes called blocking f.ii. Good technique for achieving control over the matching variable f.iii. Should be used if one is interested in the differences produced by the various levels of the extraneous variable and other independent variables f.iv. Statistical control- control of measured extraneous variables during data analysis g. Matching by Yoked Control
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Chapter 7 - Chapter 7 Control Techniques in Experimental...

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