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Chapter 3
Conﬁdence Interval About the Mean Using
the TINV Function and Hypothesis Testing
This chapter focuses on two ideas: (1) ﬁnding the 95% conﬁdence interval about the
mean, and (2) hypothesis testing.
Let’s talk about the conﬁdence interval ﬁrst.
3.1 Conﬁdence Interval About the Mean
In statistics, we are always interested in estimating the population mean. How do
we do that?
3.1.1 How to Estimate the Population Mean
Objective : To estimate the population mean,
m
Remember that the population mean is the average of all of the people in the
target population. For example, if we were interested in how well adults ages 25-44
liked a new ﬂavor of Ben & Jerry’s ice cream, we could never ask this question of
all of the people in the U.S. who were in that age group. Such a research study
would take way too much time to complete and the cost of doing that study would
be prohibitive.
So, instead of testing everyone in the population, we take a sample of people in
the population and use the results of this sample to estimate the mean of the entire
population. This saves both time and money. When we use the results of a sample to
estimate the population mean, this is called “ inferential statistics ” because we are
inferring the population mean from the sample mean.
When we study a sample of peopl e i n science research, we know the size of our
sample (n), the mean of our sample ( X ), and the standard deviation of our sample
T.J. Quirk et al., Excel 2007 for Biological and Life Sciences Statistics ,
DOI 10.1007/978-1-4614-6003-9_3, # Springer Science+Business Media New York 2013
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