A researcher has developed a new drug designed to reduce blo

A researcher has developed a new drug designed to reduce blood pressure. In an experiment, 21 subjects were assigned randomly to the treatment group and received the new experimental drug. The other 23 subjects were assigned to the control group and received a standard, well-known treatment. After a suitable period, the reduction of blood pressure for each subject was recorded. A summary of these data is:

Treatment group (new drug)                                      n=21           xbar=23.48          s=8.01

Control group (old drug)                                            n=23           xbar=18.52          s=7.15

Without using software, how would you estimate the number of degrees of freedom for this problem?

a. Use the larger value, 23, chosen from the two options 21 and 23.

b. Use the smaller value, 20, chosen from the two options 20 and 22.

c. Use the smaller value, 21, chosen from the two options 21 and 23.

d. Use the larger value, 22, chosen from the two options 20 and 22.

Solution

We use the smaller value of n, 21. This is to get the higher critical t value, that is, playing it \"safe\".

Thus,

df = n - 1 = 20.

Hence, it is OPTION B: Use the smaller value, 20, chosen from the two options 20 and 22. [ANSWER, B]