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Experimentation

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Variables Variable = an aspect of events or things that differs according to the particular event or thing being considered but has a particular value for a given event or thing at a given time Variable = an aspect of events or things that differs according to the particular event or thing being considered but has a particular value for a given event or thing at a given time Ex. Variable = weight Things = persons Different persons weigh different amounts but a single person weighs a certain amount at a given time. Ex. Variable = weight Things = persons Different persons weigh different amounts but a single person weighs a certain amount at a given time.

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Variables are Pervasive Every dimension by which an entity or event can be described can be considered a variable. Every dimension by which an entity or event can be described can be considered a variable.

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Experiments and Variables Experiments are conducted to attempt to find out the relationships among variables. Experiments are conducted to attempt to find out the relationships among variables.

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Quantifying Variables Variables can be quantified by measuring their different values. Variables can be quantified by measuring their different values.

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Functional Relationships Variables are functionally related when the value of one variable determines another. Variables are functionally related when the value of one variable determines another. This can be stated mathematically: Y = f (X). The value of the variable Y is a function of the value of the variable X. This can be stated mathematically: Y = f (X). The value of the variable Y is a function of the value of the variable X. Ex. Running Speed = f (weight carried) Ex. Running Speed = f (weight carried)

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Experimental Design Experiments must be carefully designed to determine the functional relationships among variables. Experiments must be carefully designed to determine the functional relationships among variables. The influence of variables other than those being tested must be controlled. The influence of variables other than those being tested must be controlled.

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Experimental Variables Independent Variables Independent Variables Dependent Variables Dependent Variables Control Variables Control Variables

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Independent Variables Directly manipulated by the experimenter and determined before the experiment begins Directly manipulated by the experimenter and determined before the experiment begins Experiments are designed to see how manipulating the independent variable will effect the dependent variable. Experiments are designed to see how manipulating the independent variable will effect the dependent variable.

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Example of an Independent Variable A runner is clocked sprinting for 100 yards with a backpack 6 times carrying 0, 10, 20, 30, 40 and 50 pounds. A runner is clocked sprinting for 100 yards with a backpack 6 times carrying 0, 10, 20, 30, 40 and 50 pounds. The weight in the backpack is the independent variable The weight in the backpack is the independent variable

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Dependent Variables The values of the dependent variable are the product of the experimental conditions. The values of the dependent variable are the product of the experimental conditions. They are a function of the values of the independent variable. They are a function of the values of the independent variable. Dependent = f (Independent) Dependent = f (Independent) They are measured under each of the values of the independent variable. They are measured under each of the values of the independent variable.

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Example of a Dependent Variable A runner is clocked sprinting for 100 yards with a backpack 6 times carrying 0, 10, 20, 30, 40 and 50 pounds. A runner is clocked sprinting for 100 yards with a backpack 6 times carrying 0, 10, 20, 30, 40 and 50 pounds. The runner’s speed is the dependent variable The runner’s speed is the dependent variable

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Control Variables Control variables are set so that they cannot systematically affect the relationship between the independent and dependent variables. Control variables are set so that they cannot systematically affect the relationship between the independent and dependent variables. The average value of a control variable should not change as the independent variable changes. The average value of a control variable should not change as the independent variable changes.

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Example of Control Variables A runner is clocked sprinting for 100 yards with a backpack 6 times carrying 0, 10, 20, 30, 40 and 50 pounds. A runner is clocked sprinting for 100 yards with a backpack 6 times carrying 0, 10, 20, 30, 40 and 50 pounds. The time that the 6 races are run is a control variable and should be set so that the runner doesn’t get more and more tired with each race. The time that the 6 races are run is a control variable and should be set so that the runner doesn’t get more and more tired with each race.

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Ways of Setting Control Variables Have no variation of the control variable among different experimental conditions. Have no variation of the control variable among different experimental conditions. Have the same distribution of the control variable among the different experimental conditions. Have the same distribution of the control variable among the different experimental conditions. Have the values of the control variable randomly assigned among the different experimental conditions. Have the values of the control variable randomly assigned among the different experimental conditions.

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Variables and Hypotheses Experimental scientists must try to relate some terms of a hypothesis to dependent variables and some of them to independent variables. Experimental scientists must try to relate some terms of a hypothesis to dependent variables and some of them to independent variables.

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Hypothesis Testing A well designed experiment will permit observations under controlled conditions and reveal the relationship between independent and dependent variables and thus of the hypothetical terms. A well designed experiment will permit observations under controlled conditions and reveal the relationship between independent and dependent variables and thus of the hypothetical terms.

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© 2000 John Wiley & Sons, Inc. Davison and Neale: Abnormal Psychology, 8e Abnormal Psychology, Eighth Edition by Gerald C. Davison and John M. Neale Lecture.

© 2000 John Wiley & Sons, Inc. Davison and Neale: Abnormal Psychology, 8e Abnormal Psychology, Eighth Edition by Gerald C. Davison and John M. Neale Lecture.

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