A blood lead level of 70 mg/ml has been commonly accepted as safe. However, researchers have noted that some neurophysiological symptoms of lead poisoning appear in people whose blood lead levels are below 70 mg/ml. The article “Subclinical Neuropathy at Safe Levels of Lead Exposure” (Archives of Environmental Health [1975]: 180–183) gave the following nerve-conduction velocities for a group of workers who were exposed to lead in the workplace but whose blood lead levels were below 70 mg/ml and for a group of controls who had no exposure to lead:
Use a level 0.05 rank-sum test to determine whether there is a significant difference in
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INTRODUCTION TO STATISTICS & DATA ANALYS
- The NAEP considers that a national average of 283 is an acceptable performance. Using α = .05, run a two-tail t-test for one sample to test Ho: µ=283 for the 2019 scores. Report the t-obt, df, and p-values. Would you reject the null hypothesis that the 2019 scores come from a population with average 283? If this is the case, does it come from a population from larger or smaller average?arrow_forwardA researcher estimates that the average height of the buildings of 30 or more stories in a large city is at most 700 feet. A random sample of 10 buildings is selected, and the heights in feet are shown. At α = 0.025, is there enough evidence to reject the claim? 485 511 841 725 615 520 535 635 616 582 What is the critical value of the t?arrow_forwardLow-Birth-Weight Hospital Stays. Data on low-birthweight babies were collected over a 2-year period by 14 participating centers of the National Institute of Child Health and Human Development Neonatal Research Network. Results were reported by J. Lemons et al. in the on-line paper “Very Low Birth Weight Outcomes of the National Institute of ChildHealth and Human Development Neonatal Research Network” (Pediatrics, Vol. 107, No. 1, p. e1). For the 1084 surviving babies whose birth weights were 751– 1000 grams, the average length of stay in the hospital was 86 days, although one center had an average of 66 days and another had an average of 108 days. a. Can the mean lengths of stay be considered population means? Explain your answer.b. Assuming that the population standard deviation is 12 days, determine the z-score for a baby’s length of stay of 86 days at the center where the mean was 66 days.c. Assuming that the population standard deviation is 12 days, determine the z-score for a…arrow_forward
- An article in Knee Surgery, Sports Traumatology, Arthroscopy (2005, Vol. 13, pp. 273-279) considered arthroscopic meniscal repair with an absorbable screw. Results showed that for tears greater than 25 millimeters, 14 of 18 (78%) repairs were successful, but for shorter tears, 22 of 30 (73%) repairs were successful. A doctor would like to know if there is evidence that the success rate is greater for longer tears. The P-value for the test H0: p1 = p2 versus H1: p1 > p2 is closest to:arrow_forwardAn electrical engineer wishes to determine if, among two specific municipal buildings in town, Building “North” and Building “South”, whether the tensile strength of pipes (in psi) is not the same in each of these two buildings. A sample of pipes was chosen at random from both Building “North” and Building “South”, respectively. Using α = 0.05, which of the following statistical test, or parameter, would be best for determining whether tensile strength of pipes (in psi) is not the same in each of these two buildings? (Assume all statistical assumptions met.) a) Binomial Distribution b) Population Difference in Means (i.e., Unpaired Data) c) The Chi-Squared Test of Independence d) Population Mean Difference (i.e., Paired Data)arrow_forwardA nationwide study of undergraduate students reported that the mean number of drinks consumed per week during the spring semester is 7.96. The mean number of drinks consumed per week at USC is 7.64 (s.d.=2.55, N=412 Health services is concerned that USC students are consuming significantly more alcohol per week than the national average. Using an alpha level of .05, Is there sufficient evidence to be concerned? Be sure to select the correct critical value for the alternative hypothesis, and then use this evidence to make your conclusionarrow_forward
- The article “Differences in Susceptibilities of Different Cell Lines to Bilirubin Damage” (K. Ngai, C. Yeung, and C. Leung, Journal of Paediatric Child Health, 2000:36–45) reports an investigation into the toxicity of bilirubin on several cell lines. Ten sets of human liver cells and 10 sets of mouse fibroblast cells were placed into solutions of bilirubin in albumin with a 1.4 bilirubin/albumin molar ratio for 24 hours. In the 10 sets of human liver cells, the average percentage of cells surviving was 53.9 with a standard deviation of 10.7. In the 10 sets of mouse fibroblast cells, the average percentage of cells surviving was 73.1 with a standard deviation of 9.1. Find a 98% confidence interval for the difference in survival percentages between the two cell lines.arrow_forwardThe propagation of fatigue cracks in various aircraft partshas been the subject of extensive study in recent years.The accompanying data consists of propagation lives(flight hours/104) to reach a given crack size in fastenerholes intended for use in military aircraft (“StatisticalCrack Propagation in Fastener Holes Under SpectrumLoading,” J. Aircraft, 1983: 1028–1032):.736 .863 .865 .913 .915 .937 .983 1.0071.011 1.064 1.109 1.132 1.140 1.153 1.253 1.394a. Compute and compare the values of the sample meanand median.b. By how much could the largest sample observationbe decreased without affecting the value of themedian?arrow_forwardA survey of 90 recently delivered women on the rolls of a county welfare department revealed that 27 had a history of intrapartum or postpartum infection. Can we conclude that the population proportion with a history of intrapartum or postpartum infection is significantly less than or equal to 0.25? Let alpha = 0.05.arrow_forward
- In 1992, the U.S. Public Health Service and the Centres for Disease Control and Prevention recommended that all women of childbearing age consume 400mg of folic acid daily to reduce the risk of having a pregnancy that is affected by a neural tube defect such as spina bifida or anencephaly. In a study by Stepanuk et al. (A-3), 693 pregnant women called a teratology information service about their use of folic acid supplementation. The researchers wished to determine if preconceptional use of folic acid and race are independent. The data appear in Table below: Total Preconceptional Use of Folic Acid Race No Yes 559 299 260 White 56 41 15 Black 21 14 7 Other 636 354 282 Total Test the hypothesis that there is no association between the usage of folic acid and race with 5% significant level and using SPSS (Choose only 4 correct answers from the following statements): 1. The null and alternative hypothesis are: H0: The two variables are dependent. H1: The two…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_forwardYou are using a z-test to test H0: u=413 vs Ha: u<413 at the a=.1 level. What would the rejection region be for this test?arrow_forward
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