# PSY 452, Study Guide #7.doc - PSY 452 Study Guide for...

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PSY 452 Study Guide for Exam #7 Chapter 13: #1. Define statistics , variability, statistical inference, and statistical significance. Statistics: are quantitative measurements of samples o Descriptive stats: describe sample central tendency and variability o Inferential 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 are different o “spreads out” a sample of scores drawn from a population Statistical inference: is the process by which we make statements about a parent population based on a sample Statistical significance: results are statistically significant when the difference between our treatment groups exceeds the normal variability of scores on the DV o stat significance means that there is a treatment effect at an alpha level we have preselected, like .01 or .05 2. What is the purpose of a null hypothesis? Explain its relationship to the alternative ( also called scientific or research) hypothesis. Null hypothesis: (Ho) is the statement that the scores came from the same population and the IV did not significantly affect the DV Alternative 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 directional and a nondirectional hypothesis, and b) a one-tailed test and a two-tailed test . Directional hypothesis: predicts the “direction” of the difference between two groups on the DV o Ex: 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 o Ex: 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 .05 o The significance level is our criterion for deciding whether to accept or reject the null hypothesis o Psychologists do not use a significance level larger than .05 5. Explain the differences between a Type I error and a Type II error ( or beta 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 level Type II error (beta): is accepting the null hypothesis when it is false 6. Compare and contrast parametric and nonparametric tests. Which tests are more powerful?
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