12. Callahan (2009) demonstrated that tai chi can signifi- cantly reduce symptoms for individuals with arthritis.
Participants were 18 years old or older with doctor-
diagnosed arthritis. Self-reports of pain and stiffness
were measured at the beginning of an eight-week tai
chi course and again at the end. Suppose that the data
produced an average decrease in pain and stiffness of
Mp = 8.5 points with a standard deviation of 21.5 for
a sample of n = 40 participants.
a. Use a two-tailed test with a = .05 to determine
whether the tai chi had a significant effect on pain
and stiffness.
b. Compute Cohen's d to measure the size of the
treatment effect.