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Chapter 1: Q 1.57. (page 23)
Ideally, in stratified sampling, the members of each stratum should be relative to the characteristic under consideration.
Ideally, in stratified sampling, the members of each stratum should be homogenous to the characteristic under consideration.
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Leisure Activities and Dementia. An article appearing in the Los Angeles Timesdiscussed the study " Leisure Activities and the Risk of Dementia in the Elderly "(New England Journal of Medicine, Vol. 348, pp . 2508-2516 ) by J. Verghese et al. The article in the Times, titled "Crosswords Reduce Risk of Dementia," contained the following statement: " Elderly people who frequently read, do crossword puzzles, practice a musical instrument or play board games cut their risk of Alzheimer's and other forms of dementia by nearly two-thirds compared with people who seldom do such activities." Comment on the statement in quotes, keeping in mind the type of study for which causation can be reasonably inferred.
Immunization of Schoolchildren. In the article, "Reasons for Non - uptake of Measles, Mumps, and Rubella Catch Up Immunisation in a Measles Epidemic and Side Effects of the Vaccine" (British Medical Journal,Vol. 310, pp. 1629-1632), R. Roberts et al . discussed a follow-up survey to examine why almost 10,000 children, ages 11-15, whose records showed no previous immunization were not immunized. In the survey, 10 of the 46 schools participating in the immunization campaign were randomly chosen and then the parents of all the nonimmunized children at the 10 selected schools were sent a questionnaire. What type of sampling design was used by these authors in their survey? Explain your answer.
Regarding probability sampling:
(a) What is it?
(b) Does probability sampling always yield a representative sample?
(c) Identify some advantages of probability sampling.
Medical Testing on Animals. In its Summer 2013 Animal Action Report, the National Anti-Vivisection Society stated that "59% of Americans between the ages of 18 and 29 oppose medical testing on animals." The percentage of 59% was computed from sample data.
(a). Identify the population under consideration.
(b). Identify the sample under consideration.
(c). Is the statement in quotes descriptive or inferential?
(d). If you wanted to make it clear that the percentage of 59% was computed from sample data, how would you rephrase the statement in quotes?
Comparing Gas Mileages. An experiment is to be conducted to compare four different brands of gasoline for gas mileage.
(a) Suppose that you randomly divide 24 cars into four groups of 6 cars each and then randomly assign the four groups to the four brands of gasoline, one group per brand. Is this experimental design a completely randomized design or a randomized block design? If it is the latter, what are the blocks?
(b) Suppose, instead, that you use six different models of cars whose varying characteristics (e.g., weight and horsepower) affect gas mileage. Four cars of each model are randomly assigned to the four different brands of gasoline. Is this experimental design a completely randomized design or a randomized block design? If it is the latter, what are the blocks?
(c) Which design is better, the one in part (a) or the one in part (b)? Explain your answer.
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