Answer to Question 1
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Answer to Question 2
Internal validity exists to the extent that an experimental variable is truly responsible for any variance in the dependent variable. In other words, does the experimental manipulation truly cause changes in the specific outcome of interest? Internal validity depends in large part on successful manipulations. External validity is the accuracy with which experimental results can be generalized beyond the experimental subjects. It is increased when the subjects comprising the sample truly represent some population and when the results extend to market segments or other groups of people. The higher the external validity, the more researchers and managers can count on the fact that any results observed in an experiment will also be seen in the real world..
Marketing researchers often must trade internal validity for external validity. Laboratory experiments with many controlled factors usually are high in internal validity, while field experiments generally have less internal validity, but greater external validity. Ideally, results from lab experiments would be followed up with some type of field test.