6. It has been reported that the Kazakhs, a minority group in the Xinjiang area of China with agriculture and animal husbandry as their main employment, show a high rate of hypertension. Using a multistage sampling technique, a random sample of 1445 adult Kazakhs ( 30 years old) living in Altay, Xingjiang region of China was obtained. Among them, 536 hypertensive individuals were identified;

their daily salt intake was 18.7±13.0 (g/day), whereas that for individuals with normal blood pressure was 12.2±13.0 (g/day). Assume that daily salt intake is normally distributed, and its population variances for hypertensive and nonhypertensive Kazakh people are equal.

(a) Construct a 95% CI for the difference in the mean daily salt intake for hypertensive and nonhypertensive Kazakh people. What is the precision of the estimate?

(b) In this case, what conclusion can you draw based on the 95% CI?

(c) Describe the population about which an inference can be made.