A waterborne nonbacterial gastroenteritis outbreak occurred in Colorado as a result of a long-standing filter deficiency and malfunction of a sewage treatment plant. A study was conducted to determine whether the incidence of gastrointestinal disease during the epidemic was related to water consumption (American Water Works Journal, Jan. 1986). A telephone survey of households yielded the accompanying information on daily consumption of 8-ounce glasses of water for a sample of 40 residents who exhibited gastroenteritis symptoms during the epidemic.

a. Use a 99% confidence interval to estimate the percentage of gastroenteritis cases who drink 1–2 glasses of water per day.

b. Use a 99% confidence interval to estimate the difference between the percentages of gastroenteritis cases who drink 1–2 and 0 glasses of water per day.

c. Conduct a test to determine whether the incidence of gastrointestinal disease during the epidemic is related to water consumption. Use α = .01.