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Confounding and Internal Validity
The experimental method has the advantage of allowing a relatively unambiguous interpretation of results.
This is because the researcher manipulates the variable to create groups that differ in the of the variable and then compares the groups in terms of their scores on the variable. |
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When all other variables are held , the researcher can confidently claim that the independent variable the results and the experiment is said to have validity. |
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Basic Experiments
The basic, simple experimental design can take two forms: a only design or a pretest-posttest design. |
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Both designs require two groups of participants, of the independent variable, and measurement of the effect of the independent variable on the variable. |
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The only difference between the two experimental designs is that a pretest is given the experimental manipulation in the design. |
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Assigning Participants to Experimental Conditions: Independent Groups, Repeated Measures Designs and Matched Pairs
There are two basic ways to assign participants to experimental conditions.
One of the procedures is called an groups design. |
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Using this procedure, participants are randomly assigned to participate in only group or level of the independent variable. |
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The other procedure is called a measures design in which participants are assigned to the levels of an independent variable. |
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Compared to the independent groups design, the repeated measures design has several advantages. First, there are participants needed. |
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Secondly, this design is extremely to finding statistically significant differences between groups. However, there is also a major problem with this design that stems from the fact that the different conditions must be presented in a particular sequence. |
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The presentation sequence may have an affect on the dependent variable and the results of the study may be due to an effect rather than the effect of the independent variable. |
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Complete and extending the time interval between conditions are two approaches researchers use to deal with this problem. |
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A somewhat more complicated way to assign participants to conditions in an experiment is called a pairs design. |
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In this design, participants are first matched on a characteristic. |
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Participants that are approximately equal on the characteristic are together and then members of each pair are assigned to the conditions of the experiment. |
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This design ensures that the groups are on the matching variable prior to the introduction of the independent variable manipulation. |
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This matching procedure results in a ability to detect a statistically significant effect of the independent variable. |
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Developmental Research Designs
Developmental psychologists often study the ways that individuals change as a function of age.
They use two basic methods for studying individuals of different ages: the method and the longitudinal method. |
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A third method that is a combination of both basic methods is called the method. |
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