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Stat 20Midterm ExamInstructor: Tessa Childers-Day11 March 2014Please write your name and student ID below, and circle your section. With yoursignature, you certify that you have not observed poor or dishonest conduct on the part ofyour classmates. You also certify that you have not been a party to poor or dishonestconduct, and that the work on this exam is solely your own.Please show your workONLY in the area provided. Work outside of this area will not be consideredfor 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 ofeach page. This midterm covers the material from Lectures 1 through 13, and Homeworks1 through 6. Show your work, including labeling quantities (such as z-scores). The clearerthat your work is, the easier it is to award partial or full credit. If you do not show yourwork, you will not receive credit. You are welcome to leave your answers as fractions. Ifyou use decimals, please round all answers to two significant figures, and hold yourrounding until the final calculation.Please show your work ONLY in the areaprovided. Work outside of this area will not be considered for credit.QuestionPointsScore115211315417517Total:75
Stat 20Midterm Exam, Page 2 of 1411 March 20141. In any experiment, observational study, or sample survey, the investigator must often choose betweenseveral 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 diagnostictool 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 givetwodistinct reasonswhy this is preferable to the other methods.Solution:Any method is acceptable, so long as the two answers are indeed distinct and makesense. 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 manytrees in a woodlot in order to assess its overall condition. Listthree distinct variablesthat aforester 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, sensiblereason.(c) (4 points) The foresters wish to assess the overall condition of a large (several hundred acre) woodedlot.They estimate that there are thousands of trees in the lot, and they are unable to measureall of them. Will the foresters be performing an experimental study, an observational study, or asample survey study?Please choose one, and explain your choice.