Experimental Design, Part 1. What We Will Cover in This Section. Basic Requirements

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1 Experimental Design, Part 1 6/27/2005 P360 Experimental Design, Part 1 1 What We Will Cover in This Section Overview. Basic requirements. Problems and Issues. 6/27/2005 P360 Experimental Design, Part 1 2 Basic Requirements Two or more groups. Participants randomly assigned to treatment conditions. One or more treatment conditions. 6/27/2005 P360 Experimental Design, Part 1 3

2 Target Population Sample Frame Random Sampling Sample Group 1 Group 2 Group 3 Randomization 6/27/2005 P360 Experimental Design, Part 1 4 Basic Design Treatment Groups Independent Dependent Group 1 Group 2 Treatment (s) controlled by the experimenter Measurement(s) made after the treatments are applied. 6/27/2005 P360 Experimental Design, Part 1 5 Example #1, Laboratory Research Independent Dependent Experimental Group Rats given maternal blood Mean retrieval time: 2.25 days Control Group Rats given saline solution. Mean retrieval time: 7.00 days 6/27/2005 P360 Experimental Design, Part 1 6

3 Experimental s DEPENDENT VARIABLE The variable that is measured in an experiment. INDEPENDENT VARIABLE The treatment that the experimenter manipulates or controls. 6/27/2005 P360 Experimental Design, Part 1 7 Experimental Group Treatment Groups Group that gets some level of the treatment being studied. Control Group Group in the study that does not get the experimental treatment. Comparison Group Group in the study that gets some alternative level of the experimental treatment. 6/27/2005 P360 Experimental Design, Part 1 8 Example #2, Field Research In 1984 Pittsburgh National Bank had a problem with their tuition reimbursement program. They were paying tuition and fees for employees seeking bachelors degrees. Approximately 45% of the people did not want to work in the field in which they majored. The bank was prepared to scrap the program. 6/27/2005 P360 Experimental Design, Part 1 9

4 Example #2, Results Experimental Group Control Group Independent 342 people who attended workshop 450 people who did not attend the workshop. Dependent Job posting Applications 70% Promotions: 12% Salary/grade change: 91% Job posting Applications 23% Promotions: 3% Salary/grade change: 66% 6/27/2005 P360 Experimental Design, Part 1 10 Internal Validity The soundness in concluding a relationship between the independent and dependent variables. Can I unambiguously conclude that the independent variable caused a change in the dependent variable. 6/27/2005 P360 Experimental Design, Part 1 11 Confounding Any variable other than the independent variable that could reasonably have caused changes in the dependent variable. 6/27/2005 P360 Experimental Design, Part 1 12

5 Confounding : Example Independent Dependent Given orange juice at 9:00 AM Given distilled water at 1:00 PM Alertness two hours later. 6/27/2005 P360 Experimental Design, Part 1 13 External Validity The extent to which research results can apply to a wide range of situations. KEY IDEA: Similarity enhances external validity. 6/27/2005 P360 Experimental Design, Part 1 14 Key Learning Point Internal validity is a prerequisite for external validity. 6/27/2005 P360 Experimental Design, Part 1 15

6 Small Group Problem Assume that you have been asked to design an experiment that demonstrates that men with tattoos are seen as being more attractive than men without tattoos. Be sure to indicate all groups and variables. 6/27/2005 P360 Experimental Design, Part 1 16 Question What was the most difficult part of designing your experiment? 6/27/2005 P360 Experimental Design, Part 1 17 Operational Definition Defining a variable or condition in terms of the specific techniques or procedures used to manipulate or measure it. Thirsty Deprived of water for 12 hours. Given a teaspoon of salt and no water for 1 hour. Attractive Rated as being pretty on a ten-point scale. Over 50, balding, and wearing a bow tie. 6/27/2005 P360 Experimental Design, Part 1 18

7 Experimental Conclusion With a well designed experiment you can conclude that the Independent CAUSED changes in the Dependent. 6/27/2005 P360 Experimental Design, Part 1 19 Reactivity 6/27/2005 P360 Experimental Design, Part 1 20 Subject Reactivity A subject s behavior changes when he/she becomes aware of The research hypothesis. The treatment condition he/she is receiving. 6/27/2005 P360 Experimental Design, Part 1 21

8 Experimenter Reactivity The researcher s behavior changes as a result of his/her knowledge of the Research hypothesis. Treatment a person is getting. 6/27/2005 P360 Experimental Design, Part 1 22 Dealing With Reactivity Single Blind Design. The study is designed in such a way that the participant does not know the treatment condition (independent variable) he/she is receiving. Double Blind Design. The study is designed in such a way that neither the researcher nor the participant knows what treatment condition (independent variable) the subject is receiving. 6/27/2005 P360 Experimental Design, Part 1 23

Experimental Design. What We Will Cover in This Section. Field Research Example

Experimental Design. What We Will Cover in This Section. Field Research Example Experimental Design 7/31/2006 RES800 Experimental Design 1 What We Will Cover in This Section Overview. Basic requirements. Between subjects designs. Within subjects designs. Factorial designs. Pre-experimental