Chapter 2: Problem 17
Briefly explain why it is advisable to avoid the use of convenience samples.
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Chapter 2: Problem 17
Briefly explain why it is advisable to avoid the use of convenience samples.
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You have been asked to determine on what types of grasslands two species of birds, northern harriers and short-eared owls, build nests. The types of grasslands to be used include undisturbed native grasses, managed native grasses, undisturbed nonnative grasses, and managed nonnative grasses. You are allowed a plot of land \(500 \mathrm{~m}\) square to study. Explain how you would determine where to plant the four types of grasses. What role would randomization play in this determination? Identify any confounding variables. Would this study be considered an observational study or an experiment? (Based on the article "Response of Northern Harriers and Short-Eared Owls to Grassland Management in Illinois," Journal of Wildlife Management \([1999]: 517-523 .)\)
Swedish researchers concluded that viewing and discussing art soothes the soul and helps relieve medical conditions such as high blood pressure and constipation (AFP International News Agency, October 14,2005 ). This conclusion was based on a study in which 20 elderly women gathered once a week to discuss different works of art. The study also included a control group of 20 elderly women who met once a week to discuss their hobbies and interests. At the end of 4 months, the art discussion group was found to have a more positive attitude, to have lower blood pressure, and to use fewer laxatives than the control group. a. Why would it be important to determine if the researchers assigned the women participating in the study at random to one of the two groups? b. Explain why you think that the researchers included a control group in this study.
The article "High Levels of Mercury Are Found in Californians" (Los Angeles Times, February 9,2006 ) describes a study in which hair samples were tested for mercury. The hair samples were obtained from more than 6000 people who voluntarily sent hair samples to researchers at Greenpeace and The Sierra Club. The researchers found that nearly one-third of those tested had mercury levels that exceeded the concentration thought to be safe. Is it reasonable to generalize these results to the larger population of U.S. adults? Explain why or why not.
Doctors are concerned about young women drinking large amounts of soda and about their decreased consumption of milk in recent years ("Teenaged Girls, Carbonated Beverage Consumption, and Bone Fractures," Archives of Pediatric and Adolescent Medicine [2000]: \(610-613\) ). In parts (a)-(d), construct two questions that might be included in a survey of teenage girls. Each question should include possible responses from which the respondent can select. (Note: The questions as written are vague. Your task is to clarify the questions for use in a survey, not just to change the syntax!) a. How much "cola" beverage does the respondent consume? b. How much milk (and milk products) is consumed by the respondent? c. How physically active is the respondent? d. What is the respondent's history of bone fractures?
A mortgage lender routinely places advertisements in a local newspaper. The advertisements are of three different types: one focusing on low interest rates, one featuring low fees for first-time buyers, and one appealing to people who may want to refinance their homes. The lender would like to determine which advertisement format is most successful in attracting customers to call for more information. Describe an experiment that would provide the information needed to make this determination. Be sure to consider extraneous factors, such as the day of the week that the advertisement appears in the paper, the section of the paper in which the advertisement appears, or daily fluctuations in the interest rate. What role does randomization play in your design?
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