Lecture 8 One Sample Designs

# Lecture 8 One Sample Designs - Null Hypothesis Testing One...

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Sample Designs Lecture 8

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Last Week Recap Sampling distributions Sampling issues – random vs. biased The normal distributions Proportions and probability t distributions Confidence intervals Using Table C & D in your book
Today Null hypothesis testing Type I ( α ) and Type II ( β ) error 1 vs. 2 tailed tests  1 sample t test Effect size (r) t test of r vs. 0 (correlations)

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Manufacturing Example You are chief officer of “fixing stuff” in a plant  that makes nails. On average, your machines  make about 5% “bad” nails. Over the past 5 batches of 100 nails though, you  have noticed the following numbers of “bad”  nails. 11, 14, 7, 12, 6 Question: Should you shut down for a bit and fix  the machines?
Probability What is the probability of getting these results if  the machine were fine?  Sidenote: Not quite the same as, “What is the  probability the machine is broken?” To find out, we can use a “one-sample t-test” One sample significance test

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Significance? Problem with psychology What does significant really mean? The result was NOT likely to have occurred by  chance. Does it mean the result is important?  Maybe. Maybe not.
Two main questions in inferential statistics 1. Is there a significant difference? 1. If so, how big is this difference (both  statistically and practically)?

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Null Hypothesis Statistical Testing (NHST) A logical and statistical procedure for  determining whether or not a “difference” is big  enough to warrant making a particular decision.
Basic NHST Procedure 1. Identify the null and alternative hypotheses. 2. Determine what test you will perform (1 sample t test, t  test of r vs. 0, two sample t test, ANOVA, etc.) 3. Determine your alpha level, whether your test in 1 tailed  or two tailed, degrees of freedom, and find the critical t  value in Table D. Draw a picture! 4. Conduct a statistical test of the hypothesis.  5. Based on your test, make a decision on whether you will  reject or retain the null hypothesis? 6. Interpret your results in clear English (write out your  conclusion in symbols and words).

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Null Hypothesis – H 0 The hypothesis that our sample is NOT different from  the population Does are sample look like the null data? If not…
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## This note was uploaded on 05/25/2010 for the course PSYCH 11 taught by Professor Ryne during the Spring '10 term at UC Riverside.

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Lecture 8 One Sample Designs - Null Hypothesis Testing One...

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