18.sampling.stud2008

18.sampling.stud2008 - Psyc 305 Week 10 Sampling...

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Psyc 305 Week 10 Sampling Distributions
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Goals for Today’s Class We will do some of this today and some next time… 1) Review of principles important for understanding today’s class: samples and populations, random sampling and samples, hypothesis testing, p values, and how size matters 2) Sampling distribution of means 3) Hypothesis Testing with a distribution of means 4) The real logic -- or mis-logic -- of Hypothesis Testing.
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Samples and Populations Sample -- we have descriptive statistics… Population -- we estimate parameters. .. Sample Statistic Population Parameter M μ (mu) Mean Variance St Dev SD 2 2 (sigma) SD (sigma)
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Random Sampling … and we have talked about “random samples” But there is more to it…
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Hypothesis Testing Decisions We are trying to determine the truth out there in the world. .. Error Correct Decision Correct Decision Error REAL WORLD (what we don’t know but want to find out) Null H Research H True True OUR DECISION Reject Null & Go with Research H “Retain” Null (inconclusive) How can we be right? How can we make mistakes?
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Steps in Hypothesis Testing 1) State the Question as a Research Hypothesis and a Null Hypothesis about the Populations. 2) Determine the Characteristics of the Comparison Distribution. 3) Determine the Cutoff Sample Score on the Comparison Distribution at Which the Null Hypothesis Should be Rejected. 4) Determine Your Sample’s Score on the Comparison Distribution -- by finding the z score for your sample. 5) Decide Whether to Reject (or Retain) the Null Hypothesis.
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IQ Distribution at Tech In entire population --> -3 -2 -1 0 1 2 3 55 70 85 100 115 130 145 At Tech last week --> -3 -2 -1 0 1 2 3 70 80 90 100 100 120 130 This is your comparison distribution. ..
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Steps in Hypothesis Testing 3) Determine the Cutoff Sample Score on the Comparison Distribution at Which the Null Hypothesis Should be Rejected. choose a level of significance decide if it’s one-tailed or two-tailed Find the z-score for the cutoff (that your score has to be more extreme than)
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Decide One- or Two- Tailed; Find Cutoff for Z score -3 -2 -1 0 1 2 3 70 80 90 100 100 120 130 -3 -2 -1 0 1 2 3 70 80 90 100 100 120 130 If two-tailed then can “go either way”. If using 5% then divide it
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This note was uploaded on 09/25/2008 for the course PSYCH 305 taught by Professor Freeman during the Fall '08 term at UVA.

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18.sampling.stud2008 - Psyc 305 Week 10 Sampling...

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