14 - Two Independent Groups

# 14 - Two Independent Groups - Chapter 14 Testing Hypotheses...

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Chapter 14: Testing Hypotheses about Difference Between Two Independent Groups So far, we’ve compared a single sample to a population More often, we want to compare two samples to see whether they represent the same population For example, conduct an experiment where two groups are exposed to one of two conditions

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This chapter focuses on testing independent samples Samples drawn in such a way that selection of elements in one sample have no influence on selection of elements in another sample Follows from the random sampling method
In psychology, we typically don’t employ random sampling More often, use random assignment to place a sample into different conditions Though technically different, using random sample methods generally gives same result Simpler, so this is what we generally use

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Both random sampling and random assignment provides experimental control over extraneous variables Allows one to confidently move from statistical conclusion to research conclusion
Procedure for Hypothesis Test Same process as testing hypotheses about single mean Develop H 0 and H A Choose alpha Collect data from sample in each condition Compare result with relevant sampling distribution

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H 0 and H A Two Independent Samples (X and Y) Null Hypothesis is now of No Difference Between Groups – H 0 : µ X - µ Y = 0 Alternative Hypothesis is of Difference – Nondirectional: H A : µ X - µ Y ≠ 0 – Directional: H A : μ X - μ Y < 0 Note that hypotheses still reference the populations, and not the samples
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## This note was uploaded on 04/17/2008 for the course PSY 201 taught by Professor Arthur during the Spring '08 term at Purdue.

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14 - Two Independent Groups - Chapter 14 Testing Hypotheses...

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