Chapter_8_Reading_Guide - Chapter 8 Reading Guide CHAPTER...

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Chapter 8 Reading Guide 1 CHAPTER 8: EXPERIMENTAL DESIGN I. CONFOUNDING AND INTERNAL VALIDITY Reading: Read all. Summary: The advantage of experimental methodology is that it leads to relatively unambiguous causal interpretations of research results. The researcher manipulates the independent variable to create groups that differ in levels of that variable, then the researcher compares those groups on the level of the dependent variable. All variables, aside from the manipulated variable, are held constant through experimental control and randomization . If scores on the dependent variable differ after the manipulation of the independent variable, then the assumption is that the independent variable caused the results. Designing an experiment can be relatively simple but there are potential pitfalls. It is important to be wary of confounding variables (i.e., a variable that varies along with the independent variable). Good experimental design involves eliminating possible confounding that results in alternative explanations for the findings. If this happens, then the experiment has a high level of internal validity . Clarifications/Caveats: Control has to do with keeping confounds to a minimum. Remember earlier in the semester when we looked at the various studies and discussed the potential confounds . These were studies that took place outside of an experimental setting, so the real world led to other variables that could influence the relationship. In an experimental study, the researchers control potential confounds by holding them constant across conditions. Randomization should also be called random assignment. It is different from random sampling of participants. Random sampling has to do with who will be in the study; random assignment has to do with what will happen to those already enrolled. One of the easiest ways to engage in random assignment is by flipping a coin for experimental participant. Examples: Although not really an experiment, think about any diet pill advertisement you might have seen lately. Note that in the before picture, the person is usually frowning, has no tan, is dry, and is slouched down. In the after picture, the person is smiling, has a tan, is oiled down, and is posing in such a way to show muscle definition. More than just any change in weight or muscle tone is being manipulated in these ads. II. BASIC EXPERIMENTS Reading: Read all. Summary: The most simplistic experimental design has two variables: one independent variable and one dependent variable. In a basic experiment , the independent variable has two levels: the experimental group and the control group . The only difference between groups is in terms of the manipulated variable, while all other variables are controlled. There are two forms of the basic experiment: the posttest-only design and the pretest-posttest design. Clarifications/Caveats:
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This note was uploaded on 05/01/2011 for the course BB H 310 taught by Professor Beltzer,emilie during the Spring '11 term at Pennsylvania State University, University Park.

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Chapter_8_Reading_Guide - Chapter 8 Reading Guide CHAPTER...

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