Sickle-cell disease is a painful disorder of the red blood cells that in the United States affects mostly African Americans. To investigate whether the drug hydroxyurea can reduce the pain associated with sickle-cell disease, a study by the National Institutes of Health gave the drug to 150 sickle-cell sufferers and a placebo to another 150 sufferers. The researchers then counted the number of episodes of pain reported by each subject. What is the response variable in this study?

1. The presence of sickle-cell disease
2. The drug hydroxyurea
3. The number of red blood cells
4. The Number of episodes of pain

4. The number of episodes of pain.

Step-by-step explanation:

A typical experiment, usually has a response and explanatory variable. A response variable is the major problem we seek to resolve in the experiment. The explanatory variable, on the other hand, provides reasons that would explain the response variable.

In the question asked, we are trying to understand if hydroxyurea can reduce the pain suffered by sickle cell sufferers. The experiment is trying to resolve the problem of pain suffered by sickle cell sufferers. Therefore, this is the response variable.

The explanatory variable would be the drug hydroxyurea which would be used to measure and explain the response variable- the number of episodes of pain.