Toxaphene is an insecticide that has been identified as a pollutant in the Great Lakes ecosystem. To investigate the effect of toxaphene exposure on animals, groups of rats were given toxaphene in their diet. The article “Reproduction Study of Toxaphene in the Rat” (J. of Environ. Sci. Health, 1988: 101–126) reports weight gains (in grams) for rats given a low dose (4 ppm) and for control rats whose diet did not include the insecticide. The sample standard deviation for 23 female control rats was 32 g and for 20 female low-dose rats was 54 g. Does this data suggest that there is more variability in low-dose weight gains than in control weight gains? Assuming normality, carry out a test of hypotheses at significance level .05
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Chapter 9 Solutions
Probability and Statistics for Engineering and the Sciences
- The Lion’sMane. In a study by P. M.West titled “The Lion’s Mane” (American Scientist, Vol. 93, No. 3, pp. 226–236), the effects of the mane of a male lion as a signal of quality to mates and rivals was explored. Four life-sized dummies of male lions provided a tool for testing female response to the unfamiliar lions whose manes varied by length (long or short) and color (blonde or dark). The female lions were observed to see whether they approached each of the four life-sized dummies. a. experimental units. b. response variable. c. factor(s). d. levels of each factor. e. treatments.arrow_forwardThe article “Study on the Life Distribution of Microdrills” (J. of Engr. Manufacture, 2002: 301–305) reported the following observations, listed in increasing order, on drill lifetime (number of holes that a drill machines before it breaks) when holes were drilled in a certain brass alloy. 11 14 20 23 31 36 39 44 47 5059 61 65 67 68 71 74 76 78 7981 84 85 89 91 93 96 99 101 104105 105 112 118 123 136 139 141 148 158161 168 184 206 248 263 289 322 388 513 a. Why can a frequency distribution not be based on the class intervals 0–50, 50–100, 100–150, and so on? b. Construct a frequency distribution and histogram of the data using class boundaries 0, 50, 100, … , and then comment on interesting characteristics. c. Construct a frequency distribution and histogram of the natural logarithms of the lifetime observations, and comment on interesting characteristics. d. What proportion of the lifetime observations in this sample are less than 100? What proportion of the observations are at…arrow_forwardIn a study conducted in the Science Department of Faculty of Science, Technology and Human Development in a University; the researcher examined the influence of the drug succinylcholine on the circulation levels of androgens in the blood. Blood samples from wild, free-ranging deer were obtained via the jugular vein immediately after an intramuscular injection of succinylcholine using darts and a capture gun. Deer were bled again approximately 30 minutes after the injection and then released. The level of androgens at time of capture and 30 minutes later, measured in nanograms per milliliter (ng/ml), for 15 deers as in Table Q1. Assuming that the populations of androgen at time of injection and 30 minutes later are normally distributed:i) Find the average and standard deviation of this studyii)Determine the critical region of this problem.iii) Test at the 0.05 level of significance whether the androgen concentrations are altered after 30 minutes of restraint.arrow_forward
- In recent years, concerns have been expressed about adverse health effects from amalgam dental restorations, which include mercury. The table below shows results from a study in which some patients were treated with amalgam restorations and others were treated with composite restorations that do not contain mercury (based on data from “Neuropsychological and Renal Effects of Dental Amalgam in Children,” by Bellinger, et al., Journal of the American Medical Association, Vol. 295, No. 15). Use a 0.05 significance level to test for independence between the type of restoration and sensory disorders. Do amalgam restorations appear to affect sensory disorders? Amalgam Composite Sensory disorder 36 28 No sensory disorder 231 239arrow_forwardThe article “Study on the Life Distribution ofMicrodrills” (J. of Engr. Manufacture, 2002: 301–305) reported the following observations, listed inincreasing order, on drill lifetime (number of holesthat a drill machines before it breaks) when holes weredrilled in a certain brass alloy. 59 61 65 67 68 71 74 76 78 7981 84 85 89 91 93 96 99 101 104105 105 112 118 123 136 139 141 148 158161 168 184 206 248 263 289 322 388 513a. Why can a frequency distribution not be based onthe class intervals 0–50, 50–100, 100–150, andso on?b. Construct a frequency distribution and histogram ofthe data using class boundaries 0, 50, 100, … , andthen comment on interesting characteristics.c. Construct a frequency distribution and histogram ofthe natural logarithms of the lifetime observations,and comment on interesting characteristics.d. What proportion of the lifetime observations in thissample are less than 100? What proportion of theobservations are at least 200?arrow_forwardIn its January 25, 2012, issue, the Journal of the American Medical Association reported on the effects of overconsumption of low, normal, and high protein diets on weight gain, energy expenditure, and body composition. Researchers conducted a single blind, randomized controlled trial of 25 U.S. adults. The subjects were healthy, weight-stable, male and female volunteers, aged 18 to 35 years. All subjects consumed a weight-stabilizing diet for 13 to 25 days. Afterwards, the researchers randomly assigned participants to diets containing various percentages of energy from protein: 5% (low protein), 15% (normal protein), or 25% (high protein). The subjects were not aware of the specific protein level diet to which they were assigned. On these diets the researchers overfed the participants during the last 8 weeks of their 10 to 12 week stay in the inpatient metabolic unit. The goal was to investigate the effect of overconsumption of protein on weight gain, energy expenditure, and body…arrow_forward
- Stressed-Out Bus Drivers. Previous studies have shown that urban bus drivers have an extremely stressful job, and a large proportion of drivers retire prematurely with disabilities due to occupational stress. In the paper, “Hassles on the Job: A Study of a Job Intervention With Urban Bus Drivers” (Journal of Organizational Behavior, Vol. 20, pp. 199–208), G. Evans et al. examined the effects of an intervention program to improve the conditions of urban bus drivers.Amongother variables, the researchers monitored diastolic blood pressure of bus drivers in downtown Stockholm, Sweden. The data, in millimeters of mercury (mm Hg), on the WeissStats site are based on the blood pressures obtained prior to intervention for the 41 bus drivers in the study. Use the technology of your choice to do the following. a. Obtain a normal probability plot, boxplot, histogram, and stemand-leaf diagram of the data. b. Based on your results from part (a), can you reasonably apply the one-mean t-test to the…arrow_forwardA study was conducted to examine if children with autism spectrum disorder (ASD) had higher prenatal exposure to air pollution, specifically particulate matter < 2.5 g in diameter (PM2.5). Researchers obtained birth records of all children born in Los Angeles between 2000 and 2008 and linked these to the Department of Developmental Services records to determine if any of those subjects had been diagnosed with ASD or not. They used the birth addresses given in the birth records to determine the average daily PM2.5 for the third trimester for each child. The standard deviation for PM2.5 among ASD subjects was found to be 34.6 and for non-ASD subjects was 16.8. Assume PM2.5 is normally distributed. 4a. What was the study design? * Randomized Clinical Trial (RCT) * Case Report * Nested Case-Control Study * Case-Control Study * cross-sectional study Cohort Study 4B. What are the null and alternative hypotheses? 4c. What type of statistical test would you use to analyze the…arrow_forwardA sample of men and women who had passed their driver's test either the first time or the second time were surveyed, with the following results: Results of the driving testGender First time Second timeMen 126 211Women 135 178a) Do these data suggest that there is a relationship between gender and the passing of their driver’s test from which the present sample was drawn? Let alpha=.05arrow_forward
- A District manager kept track of the sales of 14 stores before the start of an advertisement campaign and after the sales campaign. Check for significant gains in sales at the 0.05 alpha level. State the hypothesis that you are checking. Summarize your results. Store number Daily sales: Pre-sales campaign Daily sales: Post-sales campaign 1 $10,000 $7,000 2 $9,000 $7,500 3 $8,500 $8,000 4 $8,000 $8,500 5 $9,000 $8,500 6 $10,000 $7,500 7 $9,000 $8,000 8 $8,000 $8,500 9 $8,500 $9,000 10 $9,000 $9,500 11 $11,000 $10,000 12 $10,000 $11,000 13 $8,000 $11,500 14 $7,000 $12,000arrow_forwardA physiologist has conducted an experiment to evaluate the effect of hormone X on sexual behavior. Ten rats were injected with hormone X and 10 other rats received a placebo injection. The number of matings was counted over a 20-minute period. The results are shown in the table below. Table 1: Data from hormone X experiment Group 1 Hormone X Group 2 Placebo X1 (X1) 2 X2 (X1) 2 8 64 5 25 10 100 6 36 12 144 3 9 6 36 4 16 6 36 7 49 7 49 8 64 9 81 6 36 8 64 5 25 7 49 4 16 11 121 8 64 84 744 56 340 a) What is the alternative hypothesis? Use a nondirectional hypothesis. b) What is the null hypothesis? c) What do you conclude? Use α = 0.05 (2-tail)arrow_forwardQ3. Kaimura et al. (2000) investigated the effects of procyanidin B-2 tonic on human hair growth after sequential use for 6 months. In one part of the study, the total hair increase (total hairs at month 6 – total hairs at month 0) in the designated scalp area was measured for a sample of 15 men treated with a placebo control and a sample of 25 men treated with a procyanidin B-2 (PB2). The data is contained in the file A2Q3.csv. (This data is simulated based on information in the paper. You must use the data in the file to carry out the analysis). Is there evidence that the total hair increase of the subjects in the procyanidin B-2 group was greater the those in the placebo control group, at the 5% level of significance? State an appropriate null and alternative hypothesis in words and symbols.arrow_forward
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