Chelation is an alternative therapy for heart disease that uses repeated intravenous administration of a human-made amino acid in combination with oral vitamins and minerals. Practitioners believe it removes calcium deposits from buildup in arteries. However, the evidence for a positive effect is anecdotal or comes from nonrandomized, uncontrolled studies. A double-blind randomized clinical trial comparing chelation to placebo used a treadmill test in which the response was the length of time until a subject experienced ischemia (lack of blood flow and oxygen to the heart muscle).
a. After 27 weeks of treatment, the sample mean time for the chelation group was 652 seconds. A 95% confidence interval for the population mean for chelation minus the population mean for placebo was -53 to 36 seconds. Explain how to interpret the confidence interval.
b. A significance test comparing the means had P-value = 0.69. Specify the hypotheses for this test, which was two-sided.
c. The authors concluded from the test,“There is no evidence to support a beneficial effect of chelation therapy” (M. Knudtson et al., JAMA, vol. 287, p. 481, 2002). Explain how this conclusion agrees with inference based on the values in the confidence interval.