Lecture 8 One Sample Designs

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

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

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