monfils 418_hypothesis testing2-2014

# monfils 418_hypothesis testing2-2014 -...

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Sta\$s\$cs and research design Chapter 7. Hypothesis tes\$ng, and z‐test, review

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Media example: z-test review Return to the example of media violence on aggressive behavior ‐ Does violent content in a video aFect subsequent responding? ‐ 100 subjects saw a video containing considerable violence. ‐ They then free associated to 26 homonyms that had an aggressive & nonaggressive form. e.g. cuF, mug, plaster, pound, sock
Results‐ Mean number of aggressive free associates = 7.10 (sample mean) Assume that we know that without aggressive video the mean would be 5.65 and the standard devia\$on = 4.5 These are popula\$on parameters ( μ and σ ) Is 7.10 enough larger than 5.65 to conclude that video aFected results? Media example: z-test review

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Sampling Distribu\$on of the Mean We need to know what kinds of sample means to expect if the video has no eFect i. e. What kinds of means can we expect if μ = 5.65 and σ = 4.5? This is the sampling distribu\$on of the mean.

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Given a popula\$on with mean = μ and standard devia\$on = σ , the sampling distribu\$on of the mean (the distribu\$on of sample means) has a mean = μ , and a standard devia\$on = σ / n The distribu\$on approaches normal as n , the sample size, increases
Demonstra\$on Let popula\$on be very skewed Draw samples of 3 and calculate means Draw samples of 10 and calculate means Plot means (see next 3 slides) Note changes in standard devia\$ons, and shapes (What about means?) Cont.

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Parent Popula\$on Cont.
Sampling Distribu\$on n = 3 Cont.

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Sampling Distribu\$on n = 10 Cont.
Demonstra\$on‐‐cont.

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monfils 418_hypothesis testing2-2014 -...

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