1
STA2023 – Chapter 24 (Comparing Means)
Skip:
“Back Into The Pool” through the end of the chapter (pages 630 – 634)
In the last chapter you learned how to make inferences for the mean (
μ
) of a single population.
This chapter
addresses making inferences for comparing two population means (
1
versus
2
).
Activity 1:
A physical therapist claims that women are more flexible than men.
She measures the flexibility of 35
randomly selected adult women in Gainesville and 45 randomly selected adult men in Gainesville by
determining the number of inches subjects could reach while sitting on the floor with their legs straight out
and back perpendicular to the ground.
The more flexible an individual is, the further they can reach.
Analysis of the sample data yielded the summary statistics shown here:
Women
Men
Sample Size
35
45
Sample Mean (in inches)
20.3
18.7
Sample St. Dev. (in inches)
2.1
3.4
A.
Describe the two populations of interest to this study.
Since there are two populations being compared, this is a 2sample study
Population 1:
Population 2:
B.
Given that the data was collected randomly, is the flexibility of women and men subjects in the study
dependent on each other, or independent of each other?
Note that the standard deviations of the populations (
1
2
,
σ
) are not known.
Therefore, we will use
the sample standard deviations (
s
1
, s
2
) in our computations.
This implies that we will be using
tprocedures, not zprocedures.
The appropriate confidence interval is called a
twosample tinterval
and the appropriate hypothesis test is called a
twosample ttest
.
Also note that the sample sizes are not equal.
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 Spring '08
 Ripol
 Statistics, Statistical hypothesis testing, Gainesville

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