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Lecture 8

PSYB01H3 Lecture Notes - Lecture 8: Demand Characteristics, Habituation, Random Assignment


Department
Psychology
Course Code
PSYB01H3
Professor
Anna Nagy
Lecture
8

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Week 10 Lecture #8 Monday, July 13, 2015
- research assignment
- methodology don’t need to come up with your own, but make sure you give
credit
- look for a standardized measure, don’t need to attach a copy,
interview/questionnaire, need to attach a draft
- only need intro and methodology, no discussion and etc, not collecting data
- only the intro and methodology counts towards the 5 pages
- secondary data is okay, not allow to obtain your own data
- result and discussion not needed
- screenshot of the psychINFO result (3 of these)
- copy of the abstract from the research that you used (HARDCOPY)
- hardcopy needs to be on time, turnitin can be “late”
Chapter 8: Experimental Design
LEARNING OBJECTIVES
Describe the relationship between a confounding variable and the internal validity of an
experiment
Explain error variance
Describe the post-test only design and the pretest-posttest design, including the
advantages and disadvantages of each design
Contrast an independent groups design with a repeated measures design
Summarize the advantages and disadvantages of using a repeated measures design
Describe a matched pairs design, and state reasons why one might use this design
CONFOUNDING AND INTERNAL VALIDITY
Internal Validity: experiment must be designed and conducted so that only the
independent variable can be the cause of the results
everything is held constant, aside from the variable you want to study
Two Ways to Manipulate Independent Variable
Vary it quantitatively
comparing diff drugs and giving tdiff dosage,
always a placebo/ control group
Vary it qualitatively
comparing psychical therapy and drugs therapy
CONFOUNDING AND INTERNAL VALIDITY
Confounding Variable: confounding occurs when the effects of the independent variable
and an uncontrolled variable are intertwined so one cannot determine which is
responsible for the effect
Confounding Variables
find more resources at oneclass.com
find more resources at oneclass.com

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Tom Rogers wanted to test a new "singalong" method to teach math to fourth graders
(e.g., "I love to multiply" to the tune of "God Bless America"). He used the singalong
method in his first period class. His sixth period students continued solving math
problems with the old method. At the end of the term, Mr. Rogers found that the first
period class scored significantly lower than the sixth period class on a mathematics
achievement test. He concluded that the singalong method was a total failure.
1. Identify the independent variable(s).
- teaching method
2. Identify the dependent variable(s).
- test result
3. Identify any confounding variable(s).
- diff times of the class (need to make sure this is controlled), the
class room environment might be different
4. Propose a method to "unconfound" the experiment.
- have the two groups doing sth identical
Error Variance
“statistical variability of scores caused by the influence of variables other than your
independent variables (extraneous or subject related variables)” (Bordens & Abbott,
2005)
Rarely possible to hold all variable constant
Subjects differ from one another
Environmental conditions fluctuate
Subjects change over time
May cause fluctuation in scores that have nothing to do with your IV (produce error variance)
(Bordens & Abbott, 2005)
Fluctuating conditions…
- need to be mindful of this
BASIC EXPERIMENTS
- no “best” design, have to choose the one best for your design with the least errors as possible
- random assignment group: large enough sample group, errors will flush out, evenly distributing
the confound to the two groups
- big differences bwt this and random selection
Posttest-Only Design
Must:
Obtain two equivalent groups of participants
Selection differences
Introduce the independent variable
Measure the effect of the independent variable on the dependent variable
POSTTEST-ONLY DESIGN
find more resources at oneclass.com
find more resources at oneclass.com
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