PSY 452 Study Guide for Exam #7Chapter 13:#1. Define statistics, variability, statistical inference, andstatistical significance.Statistics: are quantitative measurements of samplesoDescriptive stats: describe sample central tendency and variabilityoInferential stats: allows us to draw conclusions about a parent population from a sample Variability: for a set of DV measurements, there is variability when the scores aredifferent o“spreads out” a sample of scores drawn from a populationStatistical inference: is the process by which we make statements about a parent population based on a sampleStatistical significance: results are statistically significant when the difference between our treatment groups exceeds the normal variability of scores on the DVostat significance means that there is a treatment effect at an alpha level we have preselected, like .01 or .052. What is the purpose of a null hypothesis? Explain its relationship to the alternative (alsocalledscientific orresearch) hypothesis.Null hypothesis: (Ho) is the statement that the scores came from the same population and the IV did not significantly affect the DVAlternative hypothesis: (H1) is the statement that the scores came from different populations the IV significantly affected the DV 3. Explain the difference between: a) a directionaland a nondirectionalhypothesis, and b) a one-tailed testand a two-tailed test.Directional hypothesis: predicts the “direction” of the difference between two groups on the DVoEx: the experimental group will lower their systolic blood pressure more than the control group Nondirectional hypothesis: predicts that the two groups will have different values on the DV oEx: the experimental group and control group will achieve different systolic blood pressure reductions One-tailed test: has a critical region at one tail of the distribution. We use a one tailed test with a directional hypothesis Two-tailed test: has two critical regions, found at opposite ends of the distribution. We use a two tailed test with a no directional hypothesis 4. Explain how one chooses an alpha level(or level of significance).Alpha level: statistical significance means that there is a treatment effect at an alpha level we have preselected, like .01 or .05oThe significance level is our criterion for deciding whether to accept or reject the null hypothesis oPsychologists do not use a significance level larger than .055. Explain the differences between a Type I errorand a Type II error(orbeta error).
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Type I error (alpha): is rejecting the null hypothesis when it is correct. The experimenter determines the risk of a Type I error by selecting the alpha levelType II error (beta): is accepting the null hypothesis when it is false 6. Compare and contrast parametricand nonparametrictests. Which tests are more powerful?
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