It has been hypothesized that a chemical known as BW prevents colds. To test this hypothesis, 20,000 volunteers were divided into four groups. Each volunteer took a white pill every morning for one year. The contents of the pill taken by the members of each group are shown in the chart below. What is the independent variable in this experiment? *


1. % Developing Colds

2. Number of Volunteers

3. Grams of sugar

4. Grams of BW