Read the Vitamin D experiment. What variables would you need to control in order to make the experiment reliable? Scenario 2: Does vitamin D help prevent catching a cold?
A woman under a blanket and blowing her nose.
Could taking vitamin D help prevent catching a cold?
You read a blog post that claims vitamin D could help prevent people from catching a cold. You ask for volunteers at work to help you test this statement. One hundred people volunteer to take 1000 IU of vitamin D per day for 180 days and track the number of colds they get during that time. These people make up Group 1. One hundred other people volunteer to not take any vitamin D for 180 days, but to still track the number of colds they get during that time. These people make up Group 2. You do not ask any of the volunteers any questions about their health or what they do outside of work. The experiment runs the same length of time for both groups, and everyone starts on the same day. You rely on the volunteers to report if they had a cold. The results are shown in the table below.

A 3 column table with 1 row. Column 1 is unlabeled with entry Average number of colds. Column 2 is labeled Group 1 with entry 1.5. Column 3 is labeled Group 2 with entry 1.5.