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Independent group design
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- 4. Important Concepts RelatedTo Experimental Research Why psychologists conduct experiments ? • Researcher conduct experiment to test the hypothesis about causes and behavior. • Experiments allow researcher to decide whether a treatment or program effectively change behavior. Random Group Design • When random assignment to treatment conditions is used, the independent group design is called a random group design.
- 5. Important Concepts RelatedTo Experimental Research Random Assignment • Experiments in which each separate group of subject in the experiment represent a different conditions as defined by level of IV. • It uses random assignment of subject to conditions in order to prior to implementing the IV. Rationale of Independent group design • Can conduct the experiment to study treatment effect. • Ability to make between group comparison. • Use of control group to infer change in experimental group only due to treatment. Threats to internal validity • Occurrence of event between treatment condition and measurement effect. • Time span between treatment conditions and measurement effects. • Presence of plausible alternative.
- 6. Logic of experimentalresearch Experimental manipulation • Researcher manipulate an IV in an experiment to observe the effect on behavior, as assessed by the dependent variable. Experimental control • Experimental control allow researcher to make causal inference that the IV cause the effect change in DV. • Manipulation, holding condition constant, balancing. Internal validity • The IV caused the difference in behavior as measured by the DV. • Three conditions required for causal inferences; covariation, time order relationship, elimination of plausible alternative causes.
- 7. High internal validityof experiment Covariation • When to different measures of the same people , event vary to together- that is when scores on one variable covary with scores on other variable. Time order relationship • The efforts to maintain minimum possible time between treatments and measurement effects. Elimination of plausible alternative causes • When confounding occur plausible alternative explanation for the observed covariation exists, the experiment lacks internal validity. • Holding condition constant and balancing.
- 8. Elimination of plausiblealternative causes Holding condition constant • It is to make sure that the IV is the only factor that differs systematically across the group. Balancing • Balancing the difference among subject tested from heterogenous population. • Forming comparable groups at the start of experiment. Averaging • As a part of balancing the researcher averages the individual differences among subject across the group of the experiment .
- 9. Elimination of plausiblealternative Objective • Dittmar et al.(2006). • There goal was to determine whether exposure to very thin body images causes young girls experience negative experience about their own body. Sample • In the experiment small group of young girls read a story about Mira as she went shopping for clothes and prepared to go to the birthday party. Procedure • as they heard the story, the girls looked at the pictures with six scenes related to story.
- 10. Treatment conditions Condition 1Condition 2 Condition 3
- 11. Conditions of experimentaldesign IV and DV Manipulation of IV Cause effect b/w IV and DV IV: Exposure to Body Image DV: Dissatisfaction IV: Exposure to Body Image C1 C2 C3 X1 X2 X3 IV: Exposure to Body Image Barbi Eme NU O3 O2 O1
- 12. Random Assignment totreatment conditions and observation of behavior Stage 1 : Random Assignment Stage 2: Random assignment to treatment condition Stage 3: Observation of behavior Girls R1 R2 R3 X1 X2 X3 Barbi Eme NU O3 O2 O1 R1 n=17 R2 n=20 R3 n=20 R1 R2 R3
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