A researcher has developed a new drug designed to reduce blood pressure. In an e

Question

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 of time, the reduction in blood pressure for each subject was recorded. A summary of these data is:

                                                                                    n          x?         s

                        Treatment group (new drug):               21        23.48   8.01

                        Control group (old drug):                     23        18.52   7.15

A 95% confidence interval for the difference in reduction of blood pressure between these two drugs is (use Option 2, the conservative method for degrees of freedom)

A.

0.45 to 9.46 points.

B.

1.26 to 8.66 points.

C.

0.17 to 9.75 points.

D.

1.35 to 8.57 points.

Explanation / Answer

pooled standard deviation = sqrt(s1^2/n1 + s2^2/n2)

= sqrt(8.01^2/21 + 7.15^2/23)

= 2.2974

difference in means = 23.48 - 18.52 = 4.96

z-score = 1.96

95% confidence interval is

4.96 - (1.96 * 2.2974) <= u < = 4.96 - (1.682 * 2.2974)

=> 0.45 < u < 9.46

hence the correct choice is A

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