Questions: Cal studies the effects of a new vaccine and designs an experiment with two groups. Group A gets the vaccine and Group B gets a placebo shot. Which of the following would be the null hypothesis in Cal's experiment? Group A and Group B are both less likely to contract the virus. Group A and Group B are equally likely to contract the virus. Group B is less likely to contract the virus compared to Group A. Group A is less likely to contract the virus compared to Group B.

The answer is the second one: Group A and Group B are equally likely to contract the virus.

Explanation for each option:

1. Group A and Group B are both less likely to contract the virus.

   • This statement suggests that both groups have a reduced likelihood of contracting the virus, which implies an effect of the vaccine. This is not a null hypothesis, as the null hypothesis typically states that there is no effect or no difference.

2. Group A and Group B are equally likely to contract the virus.

   • This is the correct null hypothesis. The null hypothesis in an experiment is a statement that there is no effect or no difference between groups. In this case, it states that the vaccine has no effect, and both groups have the same likelihood of contracting the virus.

3. Group B is less likely to contract the virus compared to Group A.

   • This statement suggests that the placebo is more effective than the vaccine, which is a specific alternative hypothesis, not a null hypothesis.

4. Group A is less likely to contract the virus compared to Group B.

   • This statement suggests that the vaccine is effective, which is an alternative hypothesis, not a null hypothesis.

In summary, the null hypothesis is that there is no difference in the likelihood of contracting the virus between Group A and Group B.