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Chapter 1: Q 1.6. (page 7)
Fill in the following blank:
Observational studies can reveal only association, whereas experiments can help establish .
Observational studies can reveal only association, whereas experiments can help establish causation.
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Ballistic Fingerprinting. In an on-line press release, ABCNews.com reported that "...73 percent of Americans... favor a law that would require every gun sold in the United States to be test-fired first, so law enforcement would have its fingerprint in case it were ever used in a crime."
(a). Do you think that the statement in the press release is inferential or descriptive? Can you be sure?
(b). Actually, ABCNews.com conducted a telephone survey of a random national sample of 1032 adults and determined that 73% of them favored a law that would require every gun sold in the United States to be test-fired first, so law enforcement would have its fingerprint in case it were ever used in a crime. How would you rephrase the statement in the press release to make clear that it is a descriptive statement? an inferential statement?
Hepatitis B and Pancreatic Cancer.The article "Study Links Hepatitis B and Cancer of Pancreas" by D. Grady, appeared in the September 29, 2008 issue of the New York Times. It reported that, for the first time, a study showed that people with pancreatic cancer are more likely than those without the disease to have been infected with the hepatitis B virus. The study by M. Hassan et al . , titled "Association Between Hepatitis B Virus and Pancreatic Cancer" (Journal of Clinical Oncology, Vol. 26, No. 28, pp. 4557-4562) compared 476 people who had pancreatic cancer with 879 healthy control subjects. All were tested to see whether they had ever been infected with the viruses that cause hepatitis B or hepatitis C. The results were that no connection was found to hepatitis C, but the cancer patients were twice as likely as the healthy subjects to have had hepatitis B. The researchers noted, however, that "...while the study showed an association, it did not prove cause and effect. More work is needed to determine whether the virus really can cause pancreatic cancer." Explain the validity of the statement in quotes.
Baseball Scores. From ESPN MLB Scoreboard, we obtained the following major league baseball scores for August 14, 2013. Is this study descriptive or inferential? Explain your answer.
Ghost of Speciation Past. In the article, "Ghost of Speciation Past" (Nature, Vol. 435, pp. 29-31), T. Kocher looked at the origins of a diverse flock of cichlid fishes in the lakes of southeast Africa. Suppose that you wanted to select a sample from the hundreds of species of cichlid fishes that live in the lakes of southeast Africa. If you took a simple random sample from the species of each lake and combined all the simple random samples into one sample, which type of sampling design would you have used? Explain your answer.
Regarding observational studies and designed experiments:
(a) Describe each type of statistical study.
(b) With respect to possible conclusions, what important difference exists between these two types of statistical studies?
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