Callahan (2009) demonstrated that tai chi can significantly 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 MD=8.5⁢points with a standard deviation of 21.5 for a sample of n=40 participants. a. Use a two-tailed test with αα=.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.

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Confidence Intervals

When we calculate intervals in probability and statistics, it can be simply termed as finding out a confidence interval. The confidence interval is usually calculated from the data set which is observed. The value of the parameter that needs to be calculated is present here only.