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Unformatted text preview: Spring 2007  STA 4702/5701  Practice Exam #1 Name: Directions : Please read all problems carefully. The exam is worth a total of 200 points. The points for each problem are shown to the left. Good luck! 1. (15) For each of the data sets described below indicate whether the data are nonrandom missing data , missing at random , or missing completely at random by writing NRM, MAR, MCAR in the space provided. (a) A survey was taken by telephone by volunteers to estimate the proportion of US voters who would consider voting for Barack Obama in the upcoming presidential election. The survey was taken mostly in the evenings and weekends, due to limitations on the schedules of the volunteers. The proportion of respondents aged 45 to 65 was 75%. The estimated proportion in the general US population for voters of this age is around 14%. (b) Researchers were measuring mercury concentrations in salmon in the Copper River. The instrument they were using had a detection limit of 0.01 ppb, so measurements below this concentration were censored by the instrument, i.e., reported as “BDL” (below detection limit). Young fish tended to have a higher probability of having concentrations BDL, but to have the same probability of being sampled as older fish. That is, the age proportions in the sample appeared to be representative of the population at large. (c) A scientist was running test tubes of DNA samples to look for the occurrence of a rare genotype in a population of finches in the Galapagos Islands. The test tubes were arranged in order of sample number. The sample was a random sample from 5 islands. While preparing the test tubes for analysis, the necklace he was wearing caught on the corner of one of the trays and 15 tubes out of 200 were knocked over and lost. 2. Professors at a certain public university are rated by their students on a scale of 1 to 10, with one being ‘horrible’ and 10 being ‘way cool’. A faculty member who consistently receives low scores believes that the ratings are determined by how difficult the course is. She believes that students will rate professors lower if the material is difficult. Scores of difficulty range from 0 to 5, where 5 is the most difficult. Below is a regression model of 60 faculty scores for different courses by the average difficulty rating received. The SAS output is shown below: 1 Analysis of Variance Sum of Mean Source DF Squares Square F Value Pr > F Model 1 55.33573 55.33573 82.96 <.0001 Error 58 38.68592 0.66700 Corrected Total 59 94.02165 Root MSE 0.81670 RSquare 0.5885 Dependent Mean 3.30884 Adj RSq 0.5814 Coeff Var 24.68234 Parameter Estimates Parameter Standard Variable Label DF Estimate Error t Value Pr > t Intercept Intercept 1 1.58907 0.21626 7.35 <.0001 difficulty difficulty 1 0.66572 0.07309 9.11 <.0001 (a) (10) Interpret the model in terms of the question of interest, giving a meaningful definition...
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This note was uploaded on 07/14/2011 for the course STA 4702 taught by Professor Staff during the Spring '08 term at University of Florida.
 Spring '08
 Staff

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