IPS6eCh06_3_4bb

# IPS6eCh06_3_4bb - Introduction to Inference Use and Abuse...

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Introduction to Inference Use and Abuse of Tests; Power and Decision IPS Chapters 6.3 and 6.4 © 2009 W.H. Freeman and Company

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Objectives (IPS Chapters 6.3 and 6.4) Use and abuse of tests Power and inference as a decision Cautions about significance tests Power of a test Type I and II errors Error probabilities
Choosing the significance level α Factors often considered: What are the consequences of rejecting the null hypothesis (e.g., global warming, convicting a person for life with DNA evidence)? Are you conducting a preliminary study? If so, you may want a larger α so that you will be less likely to miss an interesting result. Some conventions: We typically use the standards of our field of work. There are no “sharp” cutoffs: e.g., 4.9% versus 5.1 %. It is the order of magnitude of the P-value that matters: “somewhat significant,” “significant,” or “very significant.” Cautions about significance tests

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Practical significance Statistical significance only says whether the effect observed is likely to be due to chance alone because of random sampling. Statistical significance may not be practically important. That’s because statistical significance doesn’t tell you about the magnitude of the effect, only that there is one. An effect could be too small to be relevant. And with a large enough sample size, significance can be reached even for the tiniest effect.
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• Winter '07
• Guggenberger
• Null hypothesis, Statistical hypothesis testing, Statistical significance, Statistical power, W.H. Freeman

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