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Chapter 13: Confidence Intervals – Small Samples
Note:
Observe that there is a slight difference between the answers when the
formula is used and the workbook is used. This is due to rounding.
Observe that the lower limit of the interval is negative while the upper limit
is positive. Thus, zero is included in the interval. This would imply that we
cannot say that the means are different since there is a possibility of them
being equal by the fact that zero is in the interval. That is, based on the
confidence interval, the student cannot claim that the average mpg for the
foreign and domestic compact cars are different.
Example 13-6:
Two different methods (method 1 and method 2) were
used to teach an elementary statistics course for a psychology program. A
sample of 18 scores was selected for method 1, and a sample of 23 scores
was selected for method 2. The summary results are given in
Table 13-2
.
Table 13-2:
Summary information for
Example 13-6
Construct a 95% confidence interval for the difference
(Method 1 – Method 2) in the mean scores for the two different methods.
Assume normality for the scores for the two methods and that the variances
for the population of scores for the two methods are equal.
Click here for the Small Sample Confidence Interval for the Difference Between Two Independent Means Workbook