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Simon Fraser University
STAT 100
Thomas Loughin

STAT 100 Midterm 1 Fall 2009 NAME:_______________________ ID:______________________ INSTRUCTIONS: Answer all questions on all pages. Write your answers clearly in the spaces provided. Where computations are required, you should show work. Incorrect answers without clearly-displayed work cannot be considered for partial credit. If a question calls for an explanation, provide one that is complete. Do not omit important details or include irrelevant or incorrect statements. True/False or multiple choice questions need not be accompanied by an explanation. If you have difficulty, or feel like you are working slowly, solve the easiest problems first. Total points on exam: 28 GOOD LUCK! Short answers, explain – sentence or two “So act that your principle of action might safely be made a law for the whole world.” -Immanuel Kant, philosopher (1724-1804) STAT 100 Midterm 1, Fall 2009 QUESTION 1 (6 pts) 3417 people were recently selected at random from all adult taxpayers in Canada and answered questions about the Canada Revenue Agency (CRA) assessments. A. (1 pt) What was the population for the study? Adult taxpayers in Canada B. One question was, “Do you feel that CRA assessments are accurate?” 2137 answered “Yes”. a. (1 pt)Estimate the percentage of the population that feels that the CRA assessments are accurate. 2137/3417 = 0.6254 = 62.5% (rounding to 63% is OK) b. (1 pt) Find the margin of error for the estimate. Margin of error 1/√3417=1/58.46 – 0.017 or 1.7% (rounging to 2% is OK) c. (1 pt) Explain what the margin of error tells you about the population here. We are 95% confident that the study estimates the percentage of adult taxpayers in Canada who believe assessments are accurate withingg+/- 1.7%. Alternatively, we can say that 95% confidence we believe that the percentage of adult taxpayers who feels that CRA assesments are accurate is between 60.8% and 64.2%  if given a generic interpretation without mentioning detaisl and numebrs that is give half mark Definition of margin or error C. (2 pts) Suppose that three years ago another survey of about the same size asked the same question and got an estimate that was statistically significantly lower than the current estimate. Between that survey and this one, CRA began a new program to improve their assessment accuracy. Can they claim that the new program has been successful? Explain. They cannot claim that the program is successful. The best reason is that the cause of the increase may be some other factor unrelated to the new program (a “lurking variable”) (2marks) 2 STAT 100 Midterm 1, Fall 2009 A less goood answer: statistical significance may have been accidental and the program may not have chagned anything, but unusual sampling variability resulted in very different results QUESTION 2 (4 pts) The table at right lists the number of grouse sigYear Age Gender Sightings by a wildlife manager at a certain wildlife park 1993 I M 103 1993 I F 99 over 5 years. He would like to try to figure out 1993 F F 139 whether the different ages (Adult or Immature) and 1993 F M 85 genders (Female and Male) have any effect on the 1994 I M 145 1994 I F 168 number of sightings. 1994 F F 298 1994 F M 122 1995 I M 68 A. List any response variables: 1995 I F 93 1995 F F 205 1995 F M 87 sightings 1996 I M 105 1996 I F 148 1996 F F 171 B. List any explanatory variables: 1996 F M 69 1997 I M 147 1997 I F 169 Age, gender 1997 A F 175 1997 A M 95 1998 I M 110 C. Select any variable and list its values: 1998 I F 119 1998 A F 150 1998 A M 87 4 possible answers (see table) year, or age, or gender, or sightings QUESTION 3 (2 pts) Below are some measurements and corresponding instruments for each one indicate whether it is likely to be a valid measurement (in the blank, respond YES for valid or NO for not valid) 3 STAT 100 Midterm 1, Fall 2009 A. Using movie rating (G, PG, 14A, 18A, R) to measure the appropriateness of a film for children yes B. Using length of a movie as a measure of its quality No C. Using an x-ray as a measure of the presence of a fracture yes D. Using a written driver’s test as a measure of driving ability No QUESTION 4 (6 pts) A study was performed on the effects of distractions on studying. A room at a university was set up with a sound system and a TV. Student volunteers who entered the room were exposed to either (1) loud rock music, (2) soft baroque music, (3) an adventure movie on the TV, or (4) quiet (no TV or music). The student volunteers first took a brief pre-test. The students were placed into groups according to scores on the pre-test: the top 4 formed the first group, the next 4 highest formed the second group, and so on. There were 20 volunteers, so there were 5 groups. From each group, one student was exposed to the loud rock, one to the soft baroque, one to the TV, and one to the quiet. Every student was given some materials to read and study for an hour. At the end of the hour, each student took a final test on the materials. A. (1 pt) What kind of study is this?
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