A group of researchers wants to estimate the difference in time it takes to heal enough to return to work after knee replacement surgery using two different physical therapy plans. They plan to use the data in the following table to construct a two-sample t interval.
Therapy plan A B
Mean healing time (weeks) 8.2 6.8
Standard deviation (weeks) 1.5 0.9
Number of participants 45 60
Which of the following are conditions for this type of interval?
Choose all answers that apply:
A. The times for each participant are independent of each other.
B. The distributions of times in the population are approximately normal.
C. Each sample includes equal numbers of men and women.
