In an experiment to test a new drug’s effectiveness, one group is given a larger dosage than is typically prescribed, and a second group is given a smaller dosage than is typically prescribed. Then, the results of the groups are compared to each other. What is missing that would improve this scientific design?

The dosage is the independent variable because the researchers change it between groups, and the results are the dependent variable they measure. However, neither group receives the typical prescribed dosage, so there is no baseline for comparison. Adding a control group that receives the usual dosage would help show whether the larger or smaller dose changes the drug’s effectiveness.

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