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 2-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-week 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 ExacerbationsNumber 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. Test using α = .05.
b. Find a 95% confidence interval for the true proportion of Avonex MS patients who are exacerbation free during a 2-year period.
c. Refer to part b. Is there evidence that Avonex patients are more likely to have no exacerbations than placebo patients? Explain.