For an appropriately randomized experiment, you would want a population that is broad enough to allow random selection while also being specific enough to control for variables that you want to study—in this case, the effect of diet on the activity level of dogs.
Among the provided options:
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Population #1: dogs in California – This population is quite broad and includes various breeds, ages, and sizes of dogs. This broadness allows for a good random sampling across different types of dogs, which can help in generalizing the results, but it may introduce variability due to the differences between breeds.
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Population #2: golden retrievers in Omaha, Nebraska – This option is quite specific to a single breed and location. While it allows for a controlled study of a particular breed, the narrow focus may limit generalizability to all dogs.
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Population #3: poodles in the United States – This is also quite specific, focusing on one breed across a larger area than population #2. However, it still limits the variability among the population due to focusing on just one breed.
The best choice for an appropriately randomized experiment, if you want to control for the breed variable while still being able to generalize about the effect of diet across different types of dogs, would be Population #1: dogs in California. This option allows you to randomly select from a varied group of dogs, which can help in creating a more robust and generalizable study outcome.