The principle that best shows why the conclusion by the researcher is not justified is the alternative explanations principle.
This is a principle in research that posits that a researcher cannot conclude that a phenomenon is caused by something when other things could have been the cause.
In this case, the researcher concluded that having two cars caused people to have bigger garages when it could simply be that they wanted a bigger garage for storage.
Find out more on alternative explanations at https://brainly.com/question/8946311.
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