Researchers wanted to know if secondhand tobacco smoke is a significant factor in contracting lung diseases  They conducted a study comparing the health of a group of nonsmoking spouses of smokers with that of a group of nonsmoking spouses of nonsmokers  It was discovered that the spouses of smokers were significantly more susceptible to lung diseases than were the spouses of nonsmokers
The researchers concluded that secondhand tobacco smoke is indeed a factor in the development of lung diseases
The spouses of nonsmokers are no more likely to be former smokers than are the spouses of smokers.