[PDF] 1 True-False. One can reduce the width of a confidence interval by





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Confidence Intervals.pdf

For a prescribed level of confidence (less than 75% 95% or 99% are common





ENGR 201 Statistics for Engineers HW8 Due: December 6 2017 1

Dec 6 2017 (Problem 8-14 in book) The life in hours of a 75-watt light bulb is ... Construct a 95% two-sided confidence interval on the mean life?



Confidence Intervals for the Generalized ROC Criterion

Key words: Confidence interval; Diagnostic markers; ROC curve. 0.10; m n = 25 50



Chapter 21 What is a Confidence Interval?

and it is found 42 of these children had decayed teeth. (a) point estimate of p is 42. 75. = 0.52 / 0.54 / 0.56 / 0.58. (b) 95% confidence interval of p.



t-distribution Confidence Level 60% 70% 80% 85% 90% 95% 98

Confidence Level. 60%. 70%. 80%. 85%. 90%. 95%. 98%. 99%. 99.8% 99.9%. Level of Significance. 2 Tailed. 0.40. 0.30. 0.20. 0.15. 0.10. 0.05. 0.02. 0.01.



1 True-False. One can reduce the width of a confidence interval by

2 True-False. A 95% confidence interval estimate for a population mean is determined to be 75 to 85. If the confidence level is reduced to. 80 



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Therefore the 99% confidence interval for the population mean µ is 66.69 to of 50 mathematics grades out of a total of 200 showed a mean of 75 and a.



Robust confidence intervals for median (and other percentile

Specifying centile(25 50 75) will produce the 25th 50th and 75th percentile differences. level(# ) specifies the confidence level (percent) for confidence 



1 True-False. One can reduce the width of a confidence interval by taking a smaller sample size.

2 True-False. A 95% confidence interval estimate for a population mean is determined to be 75 to 85. If the confidence level is reduced to80%, the confidence interval for becomes narrower.

3 A survey of 100 retailers revealed that the mean after-tax profit was $80,000. If we assume that the population standard deviationis $15,000, determine the 95% confidence interval estimate of the mean after-tax profit for all retailers. _________ 4 The temperature readings for 20 winter days in Grand Rapids, Michigan are normally distributed with a mean of 5.5 degrees anda standard deviation of 1.5. Determine the 90% confidence interval estimate for the winter mean temperature. _________ 5 An economist is interested in studying the incomes of consumers in a particular region. The population standard deviation isknown to be $1,000. A random sample of 50 individuals resulted in an average income of $15,000. What is the upper end point ina 99% confidence interval for the average income?Enter your answer to the nearest cent.

_________ 6 The sample size needed to estimate a population mean within 2 units with a 95% confidence when the population standarddeviation equals 8 is: a.9 b.61 c.62 d.8

7 To estimate with 99% confidence the mean of a normal population, whose standard deviation is assumed to be 6 and themaximum allowable sampling error is assumed to be 1.2, requires a random sample of size: a.166 b.165 c.164 d.163

8 The sample size needed to estimate a population mean to within 10 units was found to be 68. If the population standard deviationwas 50, then the confidence level used was: a.99% b.95% c.90% d.80%

9 True-False. In determining the sample size n needed to estimate the population mean, n decreases as the population standard deviation decreases.

PAGE 1Name: __________________Class: Date: _____________

10 A random sample of 10 college students was drawn from a large university. Their ages are 22, 17, 27, 20, 23, 19, 24, 18, 19, and24 years. Estimate the population mean with 90% confidence. _________ 11 A confidence interval was used to estimate the proportion of international students. A random sample of 72 students generatedthe following 90% confidence interval: (0.438, 0.642). Using the information above, what size sample would be necessary if wewanted to estimate the true proportion to within 0.08 using 95% confidence?

a.105 b.150 c.420 d.597

12 A sample of 150 students at a particular college showed that 45 students favor pass-fail elective courses. Provide a 95%confidence interval estimate of the proportion of the population of students who favor pass-fail grades for elective courses. _________ Enter your answer in the form (LL,UL) where LL= lower class limit and UL = upper class limit. Include the parentheses. Enter youranswers to three decimal placesPAGE 2Name: __________________Class: Date: _____________

$77060,$82940()4.9483,6.0517()$15364.1619.446,23.154()0.227,0.373()1. False2. True3. 4. 5. 6. c

7. a8. c9. True10. 11. b12. ANSWER KEY - Page 1ANSWER KEYLueker Summer2008 HW7

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