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Lecture

# Chapter 8.docx

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Department
Psychology
Course Code
PSYC 1010
Professor
Hank Davis

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Chapter 8: Confidence Intervals, Effect Size, and Statistical Power Confidence Intervals  Point estimate: a summary statistic from a sample that is just one number used as an estimate of the population parameter.  Interval estimate: based on a sample statistic and provides a range of plausible values for the population parameter  Confidence interval: an interval estimate, based on the sample statistic, that includes the population mean a certain percentage of the time, were we to sample from the same population repeatedly. Calculating confidence intervals with z Distributions Step 1: Draw a picture of a distribution that will include the confidence interval. Step 2: indicate the bounds of the confidence interval on the drawing. Step 2 ^^^^ Step 2 ^^^^ Step 3: Determine the z statistics that fall at each line marking the middle 95% Step 4: Turn the z statistic back into raw means M = - z(σ ) + M lower M M upper = z(σ )M+ M Step 5: Check that the CIs make sense  Does this interval make sense?  Does the sample mean fall in the middle of the interval? Effect size and Prep The effect of sample size on statistical significance  Statistical significance (rejecting the null hypothesis) provides only limited information about what is happening in any particular situation. Tell you that 2 groups are different.  Indeed, statistical significance only tells you that a difference, at the population level, is not zero (i.e, the null hypothesis). Which is really not that helpful.  When a hypothesis tests rejects or fails to reject the Ho, we say there has been a significant effect. This does not mean there has been a substantial effect.  The statistical significance indicates that we know this result was unlikely to have occurred by due to random sampling/a
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