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Lab 227 10/12/10
Chapter 8  Hypothesis Testing and the Ztest
What is hypothesis testing?
•
A hypothesis test is a statistical method that uses sample data to evaluate a hypothesis about a
population.
o
We evaluate whether our sample mean is different from our population mean.
o
In hypothesis testing, we can either reject or fail to reject the null hypothesis.
o
We want to find out if the difference between our sample mean and the population
mean is likely to occur by chance.
o
The null hypothesis states that the difference has likely occurred by chance.
o
The research or alternative hypothesis states that the difference is unlikely to have
occurred by chance.
•
We define a critical region in our null distribution (usually 5%). If the sample mean falls in
that region, it is unlikely that it belongs to the null distribution and therefore must belong to
the alternative distribution.
•
To compare our sample mean to the population mean, we use the sampling distribution of
the mean.
•
We compare the Z score of our sample mean, to the Z score marking the critical region.
Example 1
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 Fall '10
 Fairchild

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