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Experimental Methods, Chapter 8 (Part I) Notes

by: Marcela Leon

Experimental Methods, Chapter 8 (Part I) Notes PSYC 2950

Marketplace > University of North Texas > Psychlogy > PSYC 2950 > Experimental Methods Chapter 8 Part I Notes
Marcela Leon

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These notes cover the first half of chapter 8, Experimental Research Designs, and includes Weak vs Strong (between-participants) experimental designs.
Experimental Psychology
Alexander Yu
Class Notes
Experimental Methods, Psychology, Research Designs, Between-participants, Chapter 8
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This 4 page Class Notes was uploaded by Marcela Leon on Friday February 26, 2016. The Class Notes belongs to PSYC 2950 at University of North Texas taught by Alexander Yu in Spring 2016. Since its upload, it has received 30 views. For similar materials see Experimental Psychology in Psychlogy at University of North Texas.


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Date Created: 02/26/16
Chapter 8 (Part I) Experimental Research Design Experimental Research: Looking for cause and effect by changing the IV Research Design: The outline to look for the cause and effect Weak experimental design vs. Strong design: Weakness or Strength is determined by  Cause and effect  Internal Validity Weak Experimental Research Designs: 1. One-group Posttest-Only 2. One-group Pretest-Posttest 3. Nonequivalent Posttest-Only One-group Posttest-Only Design:  Only one group of participants is given the treatment  The participants are only given a test after the treatment Ex: A group of native Spanish speaking students are given an English course to improve their English skills and take an exam by the end of the course. Problems with this design: The students did not take an exam before the course to evaluate their individual starting skill level. Therefore, we would not be able to compare the scores of the posttest and truly determine improvement. Use for this design: This design could be used, however, if background information on the participants’ English level (the DV) and past studies on the manner by which IV (type of English course) affects DV. One-group Pretest-Posttest Design:  Only one group of participants is given the treatment  There is a test before the treatment is given  There is a test after the treatment is given Ex: A group of native Spanish speaking students take an exam assessing their English skill level before starting an English course. When the course is over, participants take an exam assessing their English skill level again to determine change. Problems with this design:  Threats to Internal Validity: o History o Maturation o Regression artifact o Attrition Use for this design: This design can be used if control over these threats is possible and if the focus is mostly on the treatment effect. Nonequivalent Posttest-Only Design:  Control group is used (not equal in variables or demographics)  Experimental group is given the treatment  Both the Experimental and the Control group are given the exam after the experimental group completes the treatment Ex: The native Spanish speaking students that take the English course had been in American English speaking classes since elementary, while the control group is a group of Spanish speaking students that recently transferred from Costa Rica. Problems with this design: The control and the experimental group are not equivalent, therefore extraneous variables are possible. There is also no test before the treatment to determine change. Use for this design: Equivalent comparison groups can be attained through random assignment. Control group: The group to which the effects of the IV on the experimental group will be compared to.  Will not receive a treatment  Natural/standard experience  Estimate counterfactual: tells us what would have happened to the participants in the experimental group if they had not been given the treatment  Control for other explanations for causation Experimental group: Will receive a treatment (IV) to determine its effects on the DV. Strong Experimental Research Designs: Experimental Designs that control for extraneous variables effectively and strongly assure cause and effect. 1. Posttest-Only Control Group (between-participants) 2. Pretest-Posttest Control Group Basic Designs:  One IV and one DV  Between-participants  Within-participants Factorial Designs:  Multiple IVs Posttest-Only Control Group Design (between-participants):  In between-participant designs participants are exposed to different experimental conditions and then are randomly assigned to their groups.  Could have more than one experimental group  Participants are only given test after treatment Ex: The native Spanish speaking students are gathered from different schools, but are all randomly assigned to either the experimental (take the English course) or control group, and take a test after the experimental group has completed the treatment. Advantages to this design:  Equivalent groups Problems with this design:  No pretest Pretest-Posttest Control Group (between-participants): • Just like Posttest-Only but participants are given test before and after treatment  4 comparisons will be made: o Experimental group- before to Control group- before o Experimental group- before to Experimental group-after o Control group-before to Control group-after o Experimental group after to Control group-after Advantages of Pretest:  Equivalent groups because of random assignment  Ceiling and floor effects can be detected because of the comparison of the tests before the treatment  Analysis of Covariance- tests the differences between the experimental and control group scores after the treatment  Assurance that the IV causes changes in the DV because of the comparison of the pretests


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