Stats 20 Spring 2014 Midterm 1 Solutions - Midterm Exam...

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Stat 20 Midterm Exam Instructor: Tessa Childers-Day 11 March 2014 Please write your name and student ID below, and circle your section. With your signature, you certify that you have not observed poor or dishonest conduct on the part of your classmates. You also certify that you have not been a party to poor or dishonest conduct, and that the work on this exam is solely your own. Please show your work ONLY in the area provided. Work outside of this area will not be considered for credit. Name: Student ID: Signature: Date: Section: 101 (10am-11am) 102 (11am-12pm) 103 (1pm-2pm) 104 (1pm-2pm) 105 (2pm-3pm) 106 (3pm-4pm) 107 (4pm-5pm) 108 (5pm-6pm) Answer the questions in the spaces provided. There are questions on the front and back of each page. This midterm covers the material from Lectures 1 through 13, and Homeworks 1 through 6. Show your work, including labeling quantities (such as z-scores). The clearer that your work is, the easier it is to award partial or full credit. If you do not show your work, you will not receive credit. You are welcome to leave your answers as fractions. If you use decimals, please round all answers to two significant figures, and hold your rounding until the final calculation. Please show your work ONLY in the area provided. Work outside of this area will not be considered for credit. Question Points Score 1 15 2 11 3 15 4 17 5 17 Total: 75
Stat 20 Midterm Exam, Page 2 of 14 11 March 2014 1. In any experiment, observational study, or sample survey, the investigator must often choose between several variables to measure a quantity of interest. (a) (4 points) If an oncologist is studying the prevalence of a specific type of cancer, as a diagnostic tool he or she may choose to use a blood test, an imaging study (X-Ray, MRI, CAT scan, etc.), or biopsy (minor exploratory surgery). Please pick which method you would use and give two distinct reasons why this is preferable to the other methods. Solution: Any method is acceptable, so long as the two answers are indeed distinct and make sense. Characteristics may include cost, invasiveness, accuracy, etcetera. 2 points per distinct, sensible reason. (b) (3 points) Foresters need quick measurements of the size of a tree, since they must measure many trees in a woodlot in order to assess its overall condition. List three distinct variables that a forester could use to measure the size of a tree. No explanations are necessary. Solution: Acceptable answers include (but are not limited to): height of tree, girth of tree, root span, root depth, average/minimum/maximum branch length. 1 point per distinct, sensible reason. (c) (4 points) The foresters wish to assess the overall condition of a large (several hundred acre) wooded lot. They estimate that there are thousands of trees in the lot, and they are unable to measure all of them. Will the foresters be performing an experimental study, an observational study, or a sample survey study? Please choose one, and explain your choice .

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