Multiple sclerosis drug. Interferons are proteins produced naturally by the human body that help fight infections and regulate the immune system. A drug developed from interferons, called Avonex, is now available for treating patients with multiple sclerosis (MS). In a clinical study, 85 MS patients received weekly injections of Avonex over a two-year period. The number of exacerbations (i.e., flare-ups of symptoms)

was recorded for each patient and is summarized in the accompanying table. For MS patients who take a placebo

(no drug) over a similar two-year period, it is known from previous studies that 26% will experience no exacerbations, 30% one exacerbation, 11% two exacerbations, 14% three exacerbations, and 19% four or more exacerbations.

Number of Exacerbations Number of Patients 0 32 1 26 2 15 3 6 4 or more 6

a. Conduct a test to determine whether the exacerbation distribution of MS patients who take Avonex differs from the percentages reported for placebo patients. Use a = .10.

b. Find a 90% confidence interval for the true percentage of Avonex MS patients who remain free of exacerbations during a two-year period.

c. Refer to part

b. Is there evidence that Avonex patients are more likely to have no exacerbations than placebo patients? Explain.