In Exercises 1.17–1.22, state whether the investigation in question is an observational study or a designed experiment. Justify your answer in each case.
Aspirin and Cardiovascular Disease. In the article by P. Ridker et al. titled “A Randomized Trial of Low-dose Aspirin in the Primary Prevention of Cardiovascular Disease in Women” (New England Journal of Medicine, Vol. 352, pp. 1293–1304), the researchers noted that “We randomly assigned 39,876 initially healthy women 45 years of age or older to receive 100 mg of aspirin or placebo on alternate days and then monitored them for 10 years for a first major cardiovascular
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Introductory Statistics (10th Edition)
- What is meant by the sample space of an experiment?arrow_forwardDo sports drinks help prevent cramps in endurance sports? At the end of a marathon, officials will ask runners if they drank water or a sports drink during the race, along with whether or not they suffered any cramps. Is this an observational study or experiment?arrow_forwardAspirin and Cardiovascular Disease. In the article by P. Ridker et al. titled “A Randomized Trial of Low-dose Aspirin in the Primary Prevention of Cardiovascular Disease inWomen” (New England Journal of Medicine, Vol. 352, pp. 1293–1304), the researchers noted that “We randomly assigned 39,876 initially healthy women 45 years of age or older to receive 100 mg of aspirin or placebo on alternate days and then monitored them for 10 years for a first major cardiovascular event (i.e., nonfatal myocardial infarction, nonfatal stroke, or death from cardiovascular causes).”arrow_forward
- Video Games. A pathological video game user (PVGU) is a video game user that averages 31 or more hours a week of gameplay. According to the article “Pathological Video Game Use among Youths: A Two-Year Longitudinal Study” (Pediatrics, Vol. 127, No. 2, pp. 319–329) by D. Gentile et al., in 2011, about 9% of children in grades 3–8 were PVGUs. Suppose that, today, seven youths in grades 3–8 are randomly selected. a. Assuming that the percentage of PVGUs in grades 3–8 is the same today as it was in 2011, determine the probability distribution for the number, X, who are PVGUs. b. Determine and interpret the mean of X. c. If, in fact, exactly three of the seven youths selected are PVGUs, would you be inclined to conclude that the percentage of PVGUs in grades 3–8 has increased from the 2011 percentage? Explain your reasoning. Hint: First consider the probability P(X ≥ 3). d. If, in fact, exactly two of the seven youths selected are PVGUs, would you be inclined to conclude that the percentage…arrow_forward3. A researcher was interested in the effects of a drug on depression. Subjects were randomly assigned to one of the three groups. Subjects in the control group received a placebo and the subjects in the two treatment groups received either a 0.2 mg or a 0.4 mg dosage of the drug. After several weeks of drug (or placebo) treatment, the researcher measured the subjects' level of depression (a low score indicating greater depression) The following data were obtained. Placebo 0.2 mg 0.4 mg 12 11 12 8 10 9 9 14 11 11 17 13 13 16 15 7 16 12 Mean of X = 10 14 12 S^2 = 5.6 8.4 4 Using 5% of significance, test the hypothesis that the three groups differ in their effectiveness.arrow_forwardKava is a beverage or extract that is made from Piper methysticum, a plant native to the western Pacific islands. Suppose that, in a randomized comparative experiment to determine if taking kava daily can reduce insomnia, a group of participants with insomnia were randomly assigned to take kava (treatment group) or a placebo (control group). After six weeks, the participants were interviewed to see if they experienced a decrease in insomnia. The table shows the results from the sample. The counts are the number of people in each group who experienced a decrease in insomnia. Group Description Population proportion Sample size Sample count Sample proportion 1 Treatment (kava) P1 n₁ = 402 x1 = 213 P₁ = 0.5299 2 Control (placebo) P2 n₂ = 521 x₂ = 121 P2 = 0.2322 Compute the standard error estimate, SE, of the difference in the sample proportions. Give your answer to at least four decimal places. 0.0438 SE = Incorrect Determine the value of the two-sample z-statistic for the difference in…arrow_forward
- Recent incidents of food contamination have caused great concern among consumers. The article “How Safe Is That Chicken?” (Consumer Reports, Jan. 2010: 19–23) reported that 35 of 80 randomly selected Perdue brand broilers tested positively for either campylobacter or salmonella (or both), the leading bacterial causes of food-borne disease, whereas 66 of 80 Tyson brand broilers tested positive. If the true proportions of non-contaminated chickens for the Perdue and Tyson brands are .50 and .25, respectively, how likely is it that the null hypothesis of equal proportions will be rejected when a .01 significance level is used and the sample sizes are both 80?arrow_forwardA researcher assembled two groups of individuals suffering from symptoms of the common cold. Group A was instructed to take a new supplement three times a day. Group B was simply advised to take over the counter remedies. At the end of the trial period, 90% of the individuals from Group A had less symptoms, and 25% of the individuals from Group B had less symptoms. a) Was this study observational or experimental? Why?b) What was the explanatory variable? What was the response variable?arrow_forwardA diabetic nurse seeks to assess the prevalence of type 2 diabetes among women in a population (age 18 to 80 years). She conveniently sampled 100 women attending antenatal care and asked them whether they had hypertension. Of the 100 pregnant women sampled, 50 consented to take part in the study and 1 had diabetes. Based on this finding, the nurse concluded that “the prevalence of diabetes among women in the population is low (2%).” A) Do you agree with the conclusion made by the diabetic nurse? Justify in not more than 100 words? B) Would you have conducted such a study differently if you had all the resources at hand (Describe in not more than 75 words).arrow_forward
- 1) Identify the type of observational study (cross-sectional, retrospective, or prospective) and explain the reason for your selection: A group of doctors studied New York City residents with and without respiratory problems. They went back in time to determine how involved they were in the New York City terrorist attacks on September 11, 2001 (Triola, 2013).arrow_forwardBASED ON THE CASE SCENARIO, ANSWER QUESTION 55-60In the leg ulcer trial, 233 patients with venous leg ulcers were randomly assigned to intervention group using a new regime treatment (Group 1) or the control group using the standard care (Group 2). Patients were treated and followed up for 3 months.The researcher would like to determine if there is any association between types of treatment for leg ulcer and ulcer status (healed or not healed) at 3 months. Which statistical method is appropriate for the above case? 1. Pearson’s correlation2. Chi square goodness of fit test3. Simple linear regression4. Chi square test for independencearrow_forwardAngioplasty is a medical procedure in which an obstructed blood vessel is widened. In some cases, a wire mesh tube, called a stent, is placed in the vessel to help it remain open. The article “Long-term Outcomes of Patients Receiving Drug-eluting Stents” (A. Philpott, D. Southern, et al., Canadian Medical Association Journal, 2009:167–174) presents the results of a study comparing the effectiveness of a bare metal stent with one that that has been coated with a drug designed to prevent reblocking of the vessel. A total of 5320 patients received bare metal stents, and of these, 841 needed treatment for reblocking within a year. A total of 1120 received drug coated stents, and 134 of them required treatment within a year. a) Find a 98% confidence interval for the differences between the proportions for drug coated stents and bare metal stents. b) Suppose that additional patients are to be treated in order to increase the precision of the confidence interval. Three sampling plans are…arrow_forward
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