A report on dental patients with temporomandibular (jaw) joint dysfunction (TMD) was published in General Dentistry (Jan/Feb. 2004). A random sample of 60 patients was selected for an experimental treatment of TMD. Prior to treatment, the patients filled out a survey on two nonfunctional jaw habits—bruxism (teeth grinding) and teeth clenching—that have been linked to TMD. Of the 60 patients, 3 admitted to bruxism, 11 admitted to teeth clenching, 30 admitted to both habits, and 16 claimed they had neither habit.
a. Describe the qualitative variable of interest in the study. Give the levels (categories) associated with the variable.
b. Construct a one-way table for the sample data.

c. Find and interpret a 95% confidence interval for the true proportion of dental patients who admit to both habits.
d. Find and interpret a 95% confidence interval for the difference between the true proportion of dental patients who admit to both habits and the true proportion of dental patients who claim they have neither habit.