Experiments and Observational Studies

A Parks Department employee wants to know if latex paint is more durable than non-latex paint. She has 50 park benches painted with latex paint and has 50 park benches painted with non-latex paint.

• Experiment

• Survey

• Observational study

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A researcher asks college students how many hours of sleep they got on an average night and examines whether the number of hours of sleep affects the students’ grades

• Experiment

• Survey

• Observational study

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To test the redesign of it’s website, an online bookseller assembled 96 users of the site and randomly divided them into two groups. One group used the new website to make a purchase and one group used the old website to make the same purchase. Users of the new site were able to complete the purchase 22% faster

• Experiment

• Survey

• Observational study

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A grocery store conducts an online study in which customers are randomly selected and asked to provide feedback on their shopping experience

• Expirement

• Survey

• Observational study

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Of observational studies, surveys, and experiments, random sampling is only important in experiments.

• True
• False

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Is diet or exercise effective in combating insomnia? Some believe that cutting out desserts can help alleviate the problem, while others recommend exercise. Forty volunteers suffering from insomnia agreed to participate in a month-long experiment. Half were randomly assigned to a special no-desserts diet; the others continued desserts as usual. Half of the people in each of these groups were randomly assigned to an exercise program, while the others did not exercise. Those who ate no desserts and engaged in exercise showed the most improvement. 

• Observational Study
• Experiment

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Researchers have linked an increase in the incidence of breast cancer in Italy to dioxin released by an industrial accident in 1976. The study identified 981 women who lived near the site of the industrial explosion and were under age 40 at the time. Fifteen of the women had developed breast cancer, at an unusually young average age of 45. Medical records showed that these women had heightened concentrations of dioxin in their blood, and that each 10-fold increase in dioxin level was associated with a doubling of the risk of breast cancer. (Science News, Aug. 3, 2002)

• Observational Study
• Experiment

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To research the effects of "dietary patterns" on blood pressure in 459 subjects, subjects were randomly assigned to three groups and had their meals prepared by dieticians. Those who were fed a diet low in fat and cholesterol and high in fruits, vegetables, and low-fat dairy foods (known as the DASH diet) lowered their systolic blood pressure by an average of 6.7 points when compared with subjects fed a control diet. 

• Observational Study
• Experiment

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The May 4, 2000, issue of Science News reported that, contrary to popular belief, depressed individuals cry no more often in response to sad situations than nondepressed people. Researchers studied 23 men and 48 women with major depression, and 9 men and 24 women with no depression. They showed the subjects a sad film about a boy whose father has died, noting whether or not the subjects cried. Women cried more often than men, but there were no significant differences between the depressed and nondepressed groups. 

• Observational Study
• Experiment

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A study is conducted to investigate the relationship between owning pets and happiness. 100 subjects are randomly selected and data on whether or not a pet is owned and a happiness score (1‐10, 10 being extremely happy) are obtained.
Is this an OBSERVATIONAL or EXPERIMENTAL study?

• Observational
• Experimental

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