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Confidence Interval

Confidence Intervals for mean; t test; hypothesis test for proportion

Confidence intervals/One sample hypothesis tests Directions: For #1, calculate and interpret the confidence interval. Please show your manual calculation or the software output. Please show your work if you calculated manually on #1. If you used statistical software, please show the output. 1: Confidence Intervals for t

Amazon.com claims that its textbook prices are cheaper than those offered by the local college bookstore. To test this claim, you randomly select 15 textbooks that are sold by both. Data File TEXTBOOK gives the prices for those 15 randomly selected textbooks at the local college bookstore and at Amazon.com.

6. Amazon.com claims that its textbook prices are cheaper than those offered by the local college bookstore. To test this claim, you randomly select 15 textbooks that are sold by both. Data File TEXTBOOK gives the prices for those 15 randomly selected textbooks at the local college bookstore and at Amazon.com. a. Construct

Tests from confidence intervals

A confidence interval for the population mean tells us which values of mean are plausible (those inside the interval) and which values are not plausible (those outside the interval) at the chosen level of confidence. You can use this idea to carry out a test of any null hypothesis. Ho:mean =Mo starting with a confidence interva

Margin of Error and Confidence Interval for a Poll

A recent poll (fictitious) reports that President Obama's "approval rating" is 52% and a statement says, "This poll has an error rate of 3%." The poll sampled 1300 people. (Note: The "3%" is the "margin of error." There is no computation of the confidence interval formula needed). This is an application of a confidence inter

AluminiCorp: Test Random Sample and Confidence Interval

AluminiCorp is a major producer of aluminum cans that produces 40 billion aluminum cans every year. You work as a quality control officer for AluminiCorp, and are responsible for ensuring that the aluminum cans produced meet certain specifications. Each can is supposed to consist of precisely 15 grams of aluminum, and the market

Repeated weighings of a specimen for a 95% confidence interval

A laboratory scale is known to have a standard deviation of = 0.001 gram in repeated weighings. Scale readings in repeated weighings are normally distributed, with mean equal to the true weight of the specimen. How many times must you weigh a specimen on this scale in order to get a margin of error no larger than +0.0005 (+ ha

Confidence Interval Validity for the Study Time of Students

A class survey in a large class for first year college students asked, "About how many minutes do you study on a typical weeknight?" The mean response of the 269 students was x (bar over the x) = 137 minutes. Suppose that we know that the study time follows a normal distribution with standard deviation = 65 minutes in the popula

Statistics: Sample variability, and Introduction to statistical inferences

1. Consider a normal population with µ = 25 and σ = 8.0. (A) Calculate the standard score for a value x of 27. (B) Calculate the standard score for a randomly selected sample of 30 with = 27. (C) Explain why the standard scores of 27 are different between A and B above 2. Assume that the mean score on

Calculate sample size, maximum error of estimate

Assume that a sample is drawn and z(?/2) = 1.96 and Ï? = 15. Answer the following questions: (A) If the Maximum Error of Estimate is 0.04 for this sample, what would be the sample size? (B) Given that the sample Size is 400 with this same z(?/2) and Ï?, what would be the Maximum Error of Estimate? (C) Wha

Finding Confidence Intervals: Golf Example

A sample of 140 golfers showed that their average score on a particular golf course was 93.38 with a standard deviation of 4.36. Answer each of the following (show all work and state the final answer to at least two decimal places): (A) Find the 90% confidence interval of the mean score for all 140 golfers. (B) Find the

A mayoral election probability

A mayoral election race is tightly contested. In a random sample of 1,100 likely voters, 572 said they were planning to vote for the current mayor. Based on this sample, what is your initial hunch? If you calculated the 95% confidence interval around the mayorâ??s current proportion of votes, would you claim with 95% confidence

Confidence Intervals: Z-Tests

Digital Switches, Inc., produces a product called the C3PO with an advertised 0.5% failure rate. A test of products shipped from the factory to the company's testing lab found a sample average failure rate of 0.45% with a sample standard deviation of 0.15% when a sample of n = 64 observations was studied. A. Calculate the ra

Random Sampling in EXCEL and Confidence Interval Estimate

The employee benefits manager of a small private university would like to estimate the proportion of full-time employees who prefer adopting the first (i.e., plan A) of three available health care plans in the coming annual enrollment period. A reliable frame of the university's employees and their tentative preferences are in t

Confidence Interva for True Mean Weight of Random Sample

A random sample of 10 miniature Tootsie Rolls was taken from a bag. Each piece was weighed on a very accurate scale. The results in grams were 3.087 3.131 3.241 3.241 3.270 3.353 3.400 3.411 3.437 3.477 (a) Construct a 90 percent confidence interval for the true mean weight. (b) What sample size would be necessary to estim

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

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

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; σ = 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

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