Question

Two new drugs were given to patients with hypertension. The first drug lowered the blood pressure of 16 patients an average of 11 points, with a standard deviation of 6 points. The second drug lowered the blood pressure of 20 other patients an average of 12 points, with a standard deviation of 8 points. Determine a 95% confidence interval for the difference in the mean reductions in blood pressure, assuming that the measurements are normally distributed with UNEQUAL variances.

THIS IS NOT THE BOOK PROBLEM

Answer 1

n1 = 16

= 11

s1 = 6

n2 = 20

= 12

s2 = 8

The population variances are not equal.

So we have to use here unpooled variance.

We have to construct a 95% confidence interval for the difference between means.

Formula is

Degrees of freedom = Min( n1 - 1 , n2 - 1) = Min( 16 - 1 , 20 - 1 ) = Min( 15 , 19) = 15

tc = 2.131 ( From t table)

( - 5.9759 , 3.9759)