A case-control study was conducted looking at the association between pet ownership and adult-onset asthma. Because environment during childhood is thought to have an impact on the risk for allergy and asthma, the study used siblings without asthma as matched controls and compared the probability of current pet ownership in the newly diagnosed asthmatic sibling to that of the nonasthmatic sibling. Which of the following tests should be used to calculate the p-value for this association?