Psychology 2080A/B Chapter Notes - Chapter 11: Random Assignment, Latin Square

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Published on 22 Apr 2013
School
Western University
Department
Psychology
Course
Psychology 2080A/B
CHAPTER 11- TRUE EXPERIMENTS, PART 1: SINGLE FACTOR DESIGNS
true experiments; the experimenter has complete control over all aspects
-random assignment is preferred because it allows one to conclude that any
other variable could be confounded with the independent variable only by
chance
-no other method of assignment of subjects to conditions permits such a
conclusion
quasi experiments: research procedure which does not meet the
requirements of true experiments
factors: the independent variables of an experiment
level: a particular value of an independent variable in an experiment
condition: a group or treatment in an experiment
treatment: another word for a condition of an experiment
The Basic Elements of a Valid Experimental Design
-when threats to validity are adequately controlled for, the experiment has
been designed
-no design can rule out all threats to validity for all time
-even though there can be no perfect experiment, two particular elements of
design provide control over so many different threats to validity that they
are basic to good experimental designs :
1. the existence of a control group or condition
2. the random allocation of subjects to groups
-in experiment is within sample, each subject experiences all conditions so
random allocation of subject to conditions is not applicable
-in such experiments the subject should experience the conditions either in
random order or in counterbalanced order
(SEE TABLE 11.1 PAGE 277 ON GOOD EXPERIMENTAL DESIGN)
Within-Subjects Designs
-is desirable when the effect of one condition will not carry over to or
contaminate another conditions of the experiment to a serious degree
-experimenters avoid within-subject designs if they believe that order or
sequence effects will be substantial
order effects: changes in a subjects performance resulting from the position
in which a condition appears in an experiment
sequence effect: changes in subjects performance resulting from interactions
among the conditions themselves
-lifting weights example
-look at example on page 281
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Document Summary

Chapter 11- true experiments, part 1: single factor designs true experiments; the experimenter has complete control over all aspects. Random assignment is preferred because it allows one to conclude that any other variable could be confounded with the independent variable only by chance. The basic elements of a valid experimental design. When threats to validity are adequately controlled for, the experiment has been designed. No design can rule out all threats to validity for all time. In experiment is within sample, each subject experiences all conditions so random allocation of subject to conditions is not applicable. In such experiments the subject should experience the conditions either in random order or in counterbalanced order (see table 11. 1 page 277 on good experimental design) Is desirable when the effect of one condition will not carry over to or contaminate another conditions of the experiment to a serious degree.

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