APPENDIX D 767 3. Randomized: Subjects were assigned to the different groups through a process of random selection, whereby they had the same chance of belonging to each group. Double-blind: The subjects did not know which of the two groups they were in, and the people who evaluated results did not know either. 4. No. Correlation does not imply causality. 5. a. Systematic b. Stratified c. Simple random sample d. Convenience e. Cluster 6. Yes. The two questions give the false impression that they are addressing very different issues. Most people would be in favor of defending marriage, so the first question is likely to receive a substantial number of “yes” responses. The second question better describes the issue and subjects are much more likely to have varied responses. 7. a. Discrete b. Ratio c. The mailed responses would be a voluntary response sample, so those with strong opinions or greater interest in the topics are more likely to respond. It is very possible that the results do not reflect the true opinions of the population of all state residents. d. Stratified e. Cluster 8. a. If they have no fat at all, they have 100% less than any other amount with fat, so the 125% figure cannot be correct. b. 686 c. 28% 9. a. Interval data; systematic sample b. Nominal data; stratified sample c. Ordinal data; convenience sample 10. Because there is less than a 1% chance of getting the results by chance, the method does appear to have statistical significance. The result of 239 boys in 291 births is a rate of 82% so it is above the 50% rate expected by chance, and it does appear to be high enough to have practical significance. The procedure appears to have both statistical significance and practical significance. Chapter 1: Cumulative Review Exercises 1. 133.0. The IQ score of 188 appears to be substantially higher than the other IQ scores. 2. 0.000122 3. 4.50 is a significantly high value. 4. -6.64 5. 1068 6. 20.25 7. 0.364 8. 0.20 9. 0.000729 10. 68,719,476,736 (or about 68,719,477,000) 11. 377,149,515,625 (or about 377,149,520,000) 12. 0.000000004096 Chapter 2 Answers Section 2-1 1. The table summarizes 1000 commute times. It is not possible to identify the exact values of all of the original data amounts. 5. The sample appears to be a convenience sample. By e-mailing the survey to a readily available group of Internet users, it was easy to obtain results. Although there is a real potential for getting a sample group that is not representative of the population, indications of which ear is used for cell phone calls and which hand is dominant do not appear to be factors that would be distorted much by a sample bias. 7. With 717 responses, the response rate is 14%, which does appear to be quite low. In general, a very low response rate creates a serious potential for getting a biased sample that consists of those with a special interest in the topic. 9. Systematic 11. Random 13. Cluster 15. Stratified 17. Random 19. Convenience 21. Observational study. The sample is a convenience sample consisting of subjects who decided themselves to respond. Such voluntary response samples have a high chance of not being representative of the larger population, so the sample may well be biased. The question was posted in an electronic edition of a newspaper, so the sample is biased from the beginning. 23. Experiment. This experiment would create an extremely dangerous and illegal situation that has a real potential to result in injury or death. It’s difficult enough to drive in New York City while being completely sober. 25. Experiment. The biased sample created by using a small sample of college students cannot be fixed by using a larger sample. The larger sample will still be a biased sample that is not representative of the population of all adults. 27. Observational study. Respondents who have been convicted of felonies are not likely to respond honestly to the second question. The survey will suffer from a “social desirability bias” because subjects will tend to respond in ways that will be viewed favorably by those conducting the survey. 29. Prospective study 31. Cross-sectional study 33. Matched pairs design 35. Completely randomized design 37. a. Not a simple random sample, but it is a random sample. b. Simple random sample and also a random sample. c. Not a simple random sample and not a random sample. Chapter 1: Quick Quiz 1. No. The numbers do not measure or count anything. 2. Nominal 3. Continuous 4. Quantitative data 5. Ratio 6. Statistic 7. No 8. Observational study 9. The subjects did not know whether they were getting aspirin or the placebo. 10. Simple random sample Chapter 1: Review Exercises 1. The respondents are a voluntary response sample or a self- selected sample. Because those with strong interests in the topic are more likely to respond, it is very possible that their responses do not reflect the opinions or behavior of the general population. 2. a. The sample is a voluntary response sample, so the results are questionable. b. Statistic c. Observational study
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