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CHAPTER 8, EXPERIMENTS

Chapter Outline

Topics Appropriate to Experiments The Classical Experiment Selecting Subjects Variations on Experimental Design An Illustration of Experimentation An Illustration of Experimentation Web-Based Experiments Natural Experiments Strengths and Weaknesses of the Experimental

Method Ethics and Experiments Quick Quiz

Experiments involve: Taking actionObserving consequences of that action

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Topics Appropriate to Experiments

Well-suited for projects involving limited and well-defined concepts and propositions.Hypothesis testingyp gBetter suited for explanatory than

descriptiveSmall group interaction

The Classical Experiment

Major Components1. Independent and Dependent Variables2. Pre-testing and Post-testing3. Experimental and Control Groups3. Experimental and Control Groups

Independent and Dependent Variables Independent Takes the form of a stimulus

(present or absent), cause

Dependent - Effect

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Pre-testing The measurement of a dependent variable along subjects.

Post-testing The measurement of a Post testing The measurement of a dependent variable among subjects after they have been exposed to an independent variable.

Experimental Group A group of subjects to whom an experimental stimulus is administered.

Control Group A group of subjects to whom no experimental stimulus is administered and who should resemble the experimental group in all other respects.

Figure 8.1

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Hawthorne Effect

The Double-Blind Experiment An experimental design in which neither the subjects nor the experimenters know which is the experimental and which is the control group.

Selecting Subjects

Role of college students

Generalizability? Generalizability?

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Probability Sampling

Randomization A technique for assigning experimental subjects to experimental and control groups.g p

Matching The procedure whereby pairs of subjects are matched on the basis of their similarities on one or more variables, and one member of the pair is assigned to the experimental group and the other to the control group.

Figure 8.2

Variations on Experimental Design Pre-experimental Research Designs One-shot case study A single group of

subjects is measured on a dependent variable following an experimental stimulus.

One-group pre-test post-test design A pre-test is added for the experimental group but lacks a control group.

Static-group comparison Includes experimental and control groups, but no pre-test.

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Figure 8.3

Validity Issues in Experimental Research Internal Validity The possibility that the

conclusions drawn from experimental results may not accurately reflect what went on in the experiment itself. Sources: history, maturation, testing,

instrumentation, statistical regression, selection bias, experimental mortality, causal time order, diffusion or imitation of treatments, compensation, compensatory rivalry, demoralization

External Validity The possibility that conclusions drawn from experimental results may not be generalizable to the real world

Figure 8.4

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Figure 8.5

An Illustration of Experimentation

Field Experiments

Web-Based Experiments

Representative samples are not essentialtherefore, volunteers may be used.

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Natural Experiments

Experiments that occur outside controlled settings.

Strengths and Weaknesses of the Experimental Method

Strengths of Experimental Method Isolation of experimental variables impact

over time.Replicationp

Weaknesses of Experimental MethodArtificiality of laboratory settings

Quick Quiz

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1. In the simplest experimental design,subjects are measured in terms of a/n_____ variable exposed to a/n _____variable.A. pre-test; post-testB. post-test, pre-testC. independent; dependentD. dependent; independent

Answer: D.In the simplest experimental design,subjects are measured in terms of adependent variable exposed to andepe de t a ab e e posed to aindependent variable.

2. _____ groups are groups of subjects towhom an experimental stimulus isadministered.A. ControlCo t oB. ExperimentalC. PurposiveD. Pre-test

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Answer: B.Experimental groups are groups of

subjects to whom an experimental stimulus is administered.

3. _____ is a technique for assigning experimental subjects to experimental and control groups randomly.A. Nonprobability analyseso p obab ty a a ysesB. MatchingC. RandomizationD. Controlling

Answer: C.Randomization is a technique for assigningexperimental subjects to experimental andcontrol groups randomly.co t o g oups a do y

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4. Experiments are especially well-suitedfor research projects involving:A. limited conceptsB well-defined conceptsB. well defined conceptsC. hypothesis testingD. all of the above choices

Answer: D.Experiments are especially well-suited forresearch projects involving limitedconcepts, well-defined concepts, andco cepts, e de ed co cepts, a dhypothesis testing.

5. _____ refers to the possibility that theconclusion drawn from experimentalresults may not accurately reflect whathas gone on in the experiment itself.A. ExclusionB. Internal validityC. External validityD. Representativeness

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Answer: B.Internal validity refers to the possibilitythat the conclusion drawn fromexperimental results may not accuratelyexperimental results may not accuratelyreflect what has gone on in theexperiment itself.

6. Which of the following is the chiefadvantage of a controlled experiment?A. They require little time.B They require little moneyB. They require little money.C. They are artificial.D. The experimental variable is isolated.

Answer: D.The isolation of the experimental variable is the chief advantage of a controlled experiment.e pe e t