The BBC News website reported in 2003 that "Tight Ties Could Damage Eyesight," citing that "researchers from the New York Eye and Ear Infirmary in New York tested 40 men, half of whom were healthy, and half of whom had already been diagnosed with glaucoma. Their 'intraocular pressure' was measured, then they were asked to put on a 'slightly uncomfortable' tie for 3 minutes. They were tested again, and 60% of the glaucoma patients and 70% of the healthy men were found to have significant rises in pressure. As soon as the ties were removed, the pressure fell again." The researchers warned that long-term pressure rises have been linked to the condition glaucoma, which is the most common cause of irreversible blindness in the world.12
a. The study was an experiment; what was the treatment?
b. How many subjects were in a control group receiving no treatment?
c. The reported results involve two categorical variables. Tell what they are and which is explanatory and which is response.
d. Use the information to construct a twoway table of counts, with the explanatory variable in rows and the response in columns.
e. The researchers apparently suspected that a potential confounding variable could play a role in whether a tight necktie increases intraocular pressure. What is that variable?