practice-midterm-1 - HP 340 practice midterm (answers) Fall...

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HP 340 practice midterm (answers) – Fall 2009 The exam will be closed book, closed notes, with a table of (some) formulas, and tables of critical values for the T and Z distributions like Table C.1 and C.2 in Appendix C of your textbook. In this practice exam, several of the computation exercises are pulled from the textbook; answers can be found in Appendix E. These questions may not mirror those on the exam, but if you can manage these, you should do fine on the actual midterm. You will want to flip through the slides for Chapter 9 before beginning this practice exam. Conceptual questions: 1) (Errors and intervals) At least two types of testing error are possible. a. The significance level α represents a limit for what type of error? Type I error (false positive) b. Why should experimenters ‘fail to reject the null’ in the absence of statistically significant test results? (Is this the same as accepting it?) Failure to achieve significance is not proof of the null; it may represent a Type II error (false negative) or the null may be true. c. A (1– α ) confidence interval for an estimate varies with changes in α . For example, an experimenter testing at an α level of 0.01 might be inclined to report their estimates in terms of a 99% confidence interval. How would their (1- α ) intervals change if α were increased to 0.05? The interval narrows as alpha increases. d. Which type of error occurs if a true alternative hypothesis is rejected? Type II error (false negative) 2) (Types of variables) Occasionally, an investigator will (temporarily) replace missing observations with an appropriate estimate of their expected value, often to complete exploratory analyses. A measure of central tendency – the mean, median, or mode of a variable – is often used for this purpose, but the
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This note was uploaded on 11/30/2009 for the course HP 400m at USC.

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practice-midterm-1 - HP 340 practice midterm (answers) Fall...

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