A researcher is investigating whether two weeks of caring fo…
A researcher is investigating whether two weeks of caring for a foster dog can alleviate symptoms of depression. He uses a coin flip to randomly assign 20 of the 40 subjects with depression to the treatment group who will care for a foster dog. The other 20 subjects are instructed to rest for 30 minutes each day throughout the treatment period. After two weeks, he administers a survey to assess their depression symptoms. Which of the following key principle or method of experimental design is missing?
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