Exam 1 Resolution - Biological Statistics - Fall 2008 | STAT 3615, Exams of Statistics

Download Exam 1 Resolution - Biological Statistics - Fall 2008 | STAT 3615 and more Exams Statistics in PDF only on Docsity! The honor code is strictly enforced. Please sign below to indicate that you understand both the honor code and the consequences for violating it. Your signature is your pledge that you adhered to the honor code during the exam. Printed Name :: Signature :: Directions: Show all work where appropriate, if there is no work there will be no partial credit. Keep explanations concise but clear. Be sure to state all answers in terms of the question at hand. Write down the answers of multiple choices in the table below. 14x2points 6 7 8 9 10 11 12 13 14 15 16 17 18 19 3 2 3 3 3 1 5 3or 6 2 1 1 2 1 2 1. Your adviser has asked you to summarize a set of data, which you collected in the field, that is skewed right with several outliers. You have two options, you can use either (1) the five number summary or (2) the mean and standard deviation. Which should be used and why? Be brief! Five number summary Because it showed the skewness and outliers 2. The following are a random sample of retirement ages for people at a particular company. 62; 64; 58; 45; 50; 54; 86; 73; 67; 59; 59; 48; 54; 49; 51; 53 (a) Give the Five-Number summary for these data. 45 50.5 56 63 86 (b) Compute the mean for this data. How do the mean and median compare? What does this tell you about the data? 58.25 skewed to the right 3. Babies typically learn to crawl approximately six months after birth. However, it may take longer for babies to learn to crawl in the winter, when they are often bundled in clothes that restrict their movement. Thus, there may be an association between a baby’s crawling age and the average temperature during the month they first try to crawl. Below are the average ages (in weeks) at which babies began to crawl for a sample of babies born in each of the twelve months of the year. In addition, the average temperature (in °F) for the month that is six months after the birth month is also listed. Birth month Average crawling age Average temperature January 29.84 66 February 30.52 73 March 29.70 72 April 31.84 63 May 28.58 52 June 31.44 39 July 33.64 33 August 32.82 30 September 33.83 33 October 33.35 37 November 33.38 48 December 32.32 57 We want to investigate if the average age at which infants begin to crawl (y) can be predicted from the average outdoor temperature (x) six months after birth, when they are likely to begin crawling. We decide to fit a least-squares regression line to the data with x as the explanatory variable and y as the response variable. We know the following quantities. 4) All of the above The following information is for question 8-10 A survey was designed to study how brook trout populations responded to various levels of urbanization. Urbanization had three levels: low, medium, and high impact. Historical habitats for brook trout were observed, with 200 habitats randomly selected within each level of urbanization, for a total of 600 habitats. Researchers marked each population as extirpated or present. The data are given in the following two-way table. Extirpated Present Total Low impact 25 175 200 Medium impact 80 120 200 High impact 195 5 200 8. What percentage of all historical brook trout populations were found to be extirpated in the sample? 1) 12.5% 2) 40.0% * 3) 50.0% 4) 97.5% 9. What percentage of habitats subject to medium levels of urbanization were found to be present? 1) 2.5% 2) 40.0% * 3) 60.0% 4) 87.5% 10. Which of the following conclusions seems to be supported by the data? 1) The majority of habitats subject to low urbanization impact seem to be extirpated. 2) Being classified as extirpated increases a habitat’s chance of being in a medium- rather than high-impact area. * 3) An increase in the level of urbanization impact seems to be associated with an increase in the proportion of sites that are classified as extirpated. 4) Urbanization impact level has no effect on whether or not a habitat is classified as extirpated or not. 11. If 2 quatative variables has 0 corelation, then they do not have linear relationship. 1) True * 2) False 12. Which of the following is a reason to use randomization? 1) to balance the groups on variables that you know affect the response 2) to balance the groups on lurking variables that may be unknown to you 3) to eliminate bias that may result if your assign the subjects 4) None of the above. 5) All of the above 1), 2), and 3) 13. Which of the following measures are not affected by outliers? 1) Mean and Median 2) Mean and Standard Deviation 3) Median and IQR 4) Standard Deviation and IQR 5) All of the above 6) None of the above 14. A sample was taken of the salaries of 10 employers of a large company. The following are salaries (in thousands of dollars) for this year. For convenience, the data are ordered. 28 31 34 35 37 41 42 42 42 47 Suppose each employee’s salary is increased by $3000. How will the standard deviation and mean of the salaries for the employees be changed? 1) Neither the standard deviation nor the mean will be changed. 2) The mean will increase by $3000 and the standard deviation will not be changed. 3) The mean will not be changed and the standard deviation will increase by $3000 4) The mean will increase by $3000 and the standard deviation will be multiplied by $3000. 5) The mean will increase by $3000 and the standard deviation will increase by $ 3000 . 15. Identify potential outliers, if any, for the given data using 1.5IQR rule. The test scores of 15 students are listed below. 36 40 48 65 67 69 70 73 75 76 79 82 87 90 99 1) 36 2) 99 3) 36, 99 4) 36, 40 5) 90, 99 6) None 16. A stem-and-leaf diagram is given below for the ages of the patients at a hospital. Identify the overall shape of the distribution 1) Left-skewed 2) Bimodal 3) Bell shape 4) Multimodal 5) Right-skewed 17. Which of the following numerical summary measures cannot be easily approximated from a box plot? 1) Median 2) Variance 3) Q1 4) Range 5) Interquartile range 18. Each year advertisers spend billions of dollars purchasing commercial time on network sports television. A recent article listed the top 10 leading spenders (in millions of dollars) over a 6 month period: Which of the following could not be used to graphically display the data? 1) Pie chart 2) Histogram 3) Stem-and-leaf plot 4) Dot plot 5) None of these should be used. 19. On a test John scored at the median of the class and Jim scored at the first quartile; therefore, John’s test score was twice Jim’s test score. 1) True 2) False