Ch09+Lecture

# Ch09+Lecture - CHAPTER 9 Hypothesis Testing with t Tests:...

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CHAPTER 9 Hypothesis Testing with t Tests: Comparing Two Groups

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In this Chapter > How the t distributions relate to the z distribution > How to use the t distribution table > How to conduct a single sample t test > How to conduct hypothesis tests to compare two samples Paired-samples t test (within-groups design) Independent-samples t test (between-groups design)
The t Distributions: Distributions of Means When the Parameters Are Not Known > Using t distributions Estimating a population standard deviation from a sample Sample standard deviation: ( 29 ( 29 2 1 X M s N - = -

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s = √[Σ( X - M) 2 / ( N - 1)] = √[35.2/(5 - 1)] = 8.8 = 2.97 Steps to calculating s: Calculator key:  1 xn σ -
> Calculating a t statistic for the mean of a sample Using the standard error M M M t s μ - = M s s N = where (s M = standard error)

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Figure 9-1: The Wider and Flatter t Distributions
> When sample size increases, s approaches σ and t and z become more equal > The t distributions Distributions of differences between means

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Figure 9-2: Distribution of Differences Between Means This curve represents the beginning of the development of a distribution of differences  between means. It includes only 30 differences, whereas the actual distribution would  include all possible differences.
> When would you use a z test? Give an example. > When would you use a

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## This note was uploaded on 09/30/2011 for the course PSY 3301 taught by Professor Staff during the Spring '08 term at Texas State.

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Ch09+Lecture - CHAPTER 9 Hypothesis Testing with t Tests:...

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