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# Confidence Interval

### Confidence Interval for a poll of people to sample a population

Suppose you conduct a poll if people like some product or like some TV-show. Assign your numbers for total number of people you asked (n - sample size), numbers of people who answered "yes" to the given question (n1), calculate sample proportion p = n1/n and then calculate confidence interval for population proportion. Appl

### Fact Finding trips by Congress: average cost, distribution, deviation, confidence interval

8-76. According to an investigative reporter (Jim Drinkard - Legislators want to Ground 'Fact-finding' Trips, USA Today, January 2006), members of Congress are coming under scrutiny for 'fact-finding' trips. Since 2000, members of Congress have made 6,666 trips paid for by private interests. The trips were worth about \$19.6 mill

### Confidence interval for average value for prescriptions

The BelSante Company operates retail pharmacies in 10 Eastern states. Recently, the company's internal audit department selected a random sample of 300 prescriptions issued throughout the system. The objective of the sampling was to estimate the average dollar value of all prescriptions issued by the company. The following data

### Confidence Interval estimate defined

How do I define the the population and select a simple random sample of size n from the population? A random sample of n=12 values taken from a normally distributed population resulted in the following sample value: 107 109 99 91 103 105 105 94 107 94 97 113 Use the sample information to

### Statistics 4.48 Experiment in a wave tank for mooring methods, generate electricity

4.48. An experiment was carried out on scale models in a wave tank to investigate how the choice of mooring method affected the bending stress produced in a device used to generate electricity from wave power at sea. The model system was subjected to the same sample of 18 sea states with each of the two mooring methods. The resu

### Confidence Interval for Mean and Box Plot

** Please see the attached file for the complete problem description **

### Probability

Probability In Excel 1. According to Investment Digest ("Diversification and the Risk/Reward Relationship", Winter 1994, 1-3), the mean of the annual return for common stocks from 1926 to 1992 was 19.4%, and the standard deviation of the annual return was 24.5%. During the same 67-year time span, the mean of the annual r

### Statistics: Confidence intervals for sample; Cohen's guidelines, two-tailed test

8.22. Calculate the 95% confidence interval for the following fictional data regarding daily TV viewing habits: µ = 4.7; &#963; = 1.3 hours; sample of 78 people with a mean of 4.1 hours. 8.30. For each of the following d values, identify the size of the effect using Cohen's guidelines. (a) d = 0.79 (b) d = - 0.43 (c) d = 0

### Statistics symbols, confidence intervals, z test

8.16. In statistics, concepts are often expressed in symbols and equations. For each of the following, (i) identify the incorrect symbol, (ii) state what the correct symbol should be, and (iii) explain why the initial symbol was incorrect: (a) Мlower =-z(σ) + Msample The incorrect symbol is σ. It should be σm because i

### Multiple Regression and Model Building: Zebra Wild Game advertising expenditures

See attached file. The Zebra Wild Game Company sells exotic game to high end restaurants throughout the Far East. The sales manager wants to determine what, if any, relationship exists between the pounds of game sold by 24 sales persons and two independent variables, namely, the advertising dollars spent (in hundreds of tho

### Statistics: Test for high radon levels in Florida homes for compliance to EPA standards

Historically, 10% of the homes in Florida have radon levels higher than recommended by the Environmental Protection Agency. Radon is a weakly radioactive gas known to contribute to health problems. A city in north central Florida has hired an environmental consulting group to determine whether it has a greater than normal proble

### Calculations for Hypothesis Testing and Confidence Intervals

Please see the attached problem. A manufacturing company produces water filters for home refrigerators. The process has typically produced about 4% defective. A recently designed experiment has led to changing the seal to reduce defects. With the process running using the new seal, a random sample of 300 filters yielded 7 def

### Statistics: Yaschchin discusses process for chemical etching of silicon wafers

Please see the attached problem. 2. Yaschchin (1995) discusses a process for the chemical etching of silicon wafers used in itegrated circuits. This company wishes to detect an increase in the thickness of the silicon oxide layers because thicker layers require longer etching times. Process specifications state a target valu

### Statistics 4.10: Kane discusses concentricity of engine oil seal groove

See the attached problem. 4.10. Kane (1986) discusses the concentricity of an engine oil seal groove. Historically, the standard deviation for the concentricity is 0.7. The target average concentricity is 5.6. To monitor this process, he periodically takes a random sample of three measurements. a. A recent sample yielded

### 3 Statistics problems: Sample size, mean; confidence interval for waiting time, taxes

1. The manager of Tee Shirt Emporium reports that the mean number of shirts sold per week is 1210, with a standard deviation of 325. The distribution of sales follows the normal distribution. What is the liklihood of selecting a sample of 25 weeks and finding the sample mean to be 1100 or less? 2. The manager of the local Hu

### Statistics: confidence interval estimate for university students who will return

A university planner thinks that fewer than the normal 38% of spring semester students will attend summer school. She surveys 32 current students, discovering that 12 will return to summer school. Construct a 90% confidence interval estimate for the fraction of current spring students who will return to summer school.

### Statistics: Difference in spending on textbooks at 2 universities

Please help with the following problem. Independent random samples taken on two university campuses revealed the following information concerning the average amount of money spent on textbooks during the fall semester. Develop a 95% confidence interval for the difference in spending on textbooks between students at Univ

### Statistics: estimate the proportion of the population

Part I. Suppose the coach of the football team wants to estimate the proportion of the population of fans who support his current starter lineup. The coach wants the estimate to be .04 of the true proportion. Assume a 99 percent level of confidence. The coach estimated the proportion supporting the current starter lineup to

### Constructing 95 percent confidence intervals

A reporter took a simple random sample of 725 voters in a region that has a population of 12,457. He recorded that 338 of the persons polled favored Issue 1 on the ballot. Construct a 95% confidence interval for the proportion that favor the issue and then discuss what the reporter can and cannot say in his report. If you were t

### Statistics 10 questions: Margin of error, confidence interval, sample mean, estimate

1. Use the confidence interval to find the estimated margin of error. Then find the sample mean. A biologist reports a confidence interval of (1.5, 2.9) when estimating the mean height (in centimeters) of a sample of seedlings. The estimated margin of error is _________. The sample mean is _________. 2. You work for

### Statistics 7 questions: Confidence interval, sample mean, deviation, margin of error

1. An election poll reported that a candidate had an approval rating of 45% with a margin of error E of 4%. Construct a confidence interval for the proportion of adults who approve of the candidate. The confidence interval for the proportion of adults who approve of the candidate is ____ (Round to two decimal places as neede

### Statistics: Sample size for 95% confidence level; confidence interval

Please see attached files. Please Include: The page number from the attached pdf (Chapter 9) where the appropriate formula or guidance is located on how to solve the problem. The steps involved in reaching the solution. The solution. 1 In the business research scena

### Statistics

1. Consider a normal population with a mean+ 25 and a standard deviation= 7.0. A. Calculate the standard score for a value x of 24. B. Calculate the standard score for a randomly selected sample of 45 with a sample mean = 25. C. Explain why the standard scores of 24 are different between A and B above. 2. Assume tha

### Interprete the P-value, Confidence Interval and Standard Error for the Abalone Fancy Fish Company

See the attached file. The Abalone Fancy Fish Company sells exotic fish to high end restaurants throughout the West Coast. The sales manager wants to determine what, if any, relationship exists between the pounds/week of fish sold by 24 sales persons and the length of time (in years) the sales person has been with the compan

### Confidence Intervals for thickness of paper in Fax machines and printers without jams

You are a quality analyst with John and Sons Company. Your company manufactures fax machines, copiers, and printers that use plain paper. The CEO of the company wants the machines to handle 99.5 percent of all the paper that is used in them without the paper getting jammed. The CEO asks you to determine the thickness of paper th

### Interpret confidence and prediction intervals for temperature of 44°F: Global Warming

A very broad consensus has emerged around the proposition that global warming is a reality, with likely serious global consequences. Moreover, while there is still not unanimity that global warming is entirely man-made, there is broad agreement that it is desirable to cut emissions from coal and petroleum. Finally, many energy

### Maximum error of estimate.

1. Consider a population with a mean =73.6 and a standard deviation=5.38 A. Calculate the z-score for sample mean=72.7 from a sample size of 45. B. Could this z-score be used in calculating probabilities using Table 3 in the Appendix B. Why or why not? 2. Given a level of confidence of 99% and a population standard deviatio

### Random Sample of Household Batteries for Lifetime Hours

See attached data file. Text: Data Analysis & Decision Making with Microsoft® Excel, Rev 3e, S. Christian Albright, Wayne L.Winston, Christopher J. Zappe Chapter 10 - Problem 16 A large buyer of household batteries wants to decide which of two equally priced brands to purchase. To do this, he takes a random sample of 1

### Estimate the sample size and population mean

A1) Suppose the U.S. President wants an estimate of the proportion of the population who support his current policy toward revisions in the Social Security system. The president wants the estimate to be within .04 of the true proportion. Assume a 95 percent level of confidence. The president's political advisers estimated the p

### 4 Statistics problems: Confidence interval estimate of mean

Q-3a. A stationery store wants to estimate the mean retail value of greeting cards purchased by its customers when they visit the store. A random sample of 15 customers indicates a mean amount of \$2.55 with a standard deviation of \$0.44 per customer per visit. Assuming a normal distribution, construct a 95% confidence inter