Patients with non chronic low back pain were randomly assigned to either a treatment group that received health coaching via telephone plus physiotherapy care or a control group that received only the physiotherapy care. One variable measured was improvement, over 4 weeks, in "modified Oswestry Disability Index," which is scored as a percentage, ranging from 0 to 100, with high scores representing high levels of disability. Summary statistics are shown in the table.

(a) Calculate the sample effect size from these data.
(b) A 95% confidence interval for the difference in population mean Oswestry Disability Index for the two groups (µExperimental - µControl) is (- 8.2, 18.0) percentage points. The researchers were hoping to find a difference of at least 5 percentage points, a difference that they thought would be clinically important. Based on the confidence interval, would they be ill-advised to conduct a larger study in the hope of finding convincing evidence of a 5 percentage point difference?
(c) How would your answer to (b) change if the confidence interval was (- 2.4, 3.2) percentage points.

Experimental Control Mean SD 16.8 18.7 12 11.9 11.6 14