Experimentation - Summary
Experimentation - Summary
Experiments are conducted to identify and quantify causal relationships Laboratory experiments are often relatively inexpensive and provide the opportunity to exercise tight control. In a laboratory, for example, an exposure to a concept can be controlled whereas in the more realistic field context there are many factors that can distort an exposure, such as weather, competitive reactions, and family activities. However, the laboratory experiment suffers from the testing effect and from the artificiality of the situation. Thus, the external validity (the ability to generalize from the experiment) is limited. Field experiments have greater external validity but are more costly to run (in expense, time, and security), are difficult to implement, and lack the tight control possible in the laboratory. As a result their internal validity is often a problem.
There are several experimental design alternatives to consider. The use of a control group can serve to help control for history and maturation effects. With small sample sizes, as in the use of test cities, it is useful to
match the test and control groups to reduce selection bias. The large-sample randomization, which can effectively "match" on all variables (known and unknown), is preferred. Blocking can add further control, and the Latin square provides a way to reduce the number of cells introduced by considering several control or blocking variables. Several experimental variables can be tested at once using factorial designs. Such designs provide not only main effects but also allow the analysis of interactions between experimental treatments. For example, a promotion might be very effective among urban residents but ineffective among suburban residents.
The use of a before measure increases the sensitivity of the experiment by adding another form of control; however, a before measure can serve to sensitize and bias the respondents, therefore having an effect on the after measure and on the respondent's reaction to the experimental treatment.
Experiments are conducted to identify and quantify causal relationships Laboratory experiments are often relatively inexpensive and provide the opportunity to exercise tight control. In a laboratory, for example, an exposure to a concept can be controlled whereas in the more realistic field context there are many factors that can distort an exposure, such as weather, competitive reactions, and family activities. However, the laboratory experiment suffers from the testing effect and from the artificiality of the situation. Thus, the external validity (the ability to generalize from the experiment) is limited. Field experiments have greater external validity but are more costly to run (in expense, time, and security), are difficult to implement, and lack the tight control possible in the laboratory. As a result their internal validity is often a problem.
There are several experimental design alternatives to consider. The use of a control group can serve to help control for history and maturation effects. With small sample sizes, as in the use of test cities, it is useful to
match the test and control groups to reduce selection bias. The large-sample randomization, which can effectively "match" on all variables (known and unknown), is preferred. Blocking can add further control, and the Latin square provides a way to reduce the number of cells introduced by considering several control or blocking variables. Several experimental variables can be tested at once using factorial designs. Such designs provide not only main effects but also allow the analysis of interactions between experimental treatments. For example, a promotion might be very effective among urban residents but ineffective among suburban residents.
The use of a before measure increases the sensitivity of the experiment by adding another form of control; however, a before measure can serve to sensitize and bias the respondents, therefore having an effect on the after measure and on the respondent's reaction to the experimental treatment.
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