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Confidence Interval

Confidence interval

1 (b). A survey of a random sample of 250 car commuters indicates that 80 would switch to commuting by public transport if they had to pay at least $10 per week for parking at their work places. (i) Using a 95% confidence level, calculate the confidence interval for the proportion of the commuters who might be expected to ch

Statistics: Estimate population mean at 90%, 95%, 99% confidence interval

* The UNITE/MORI 2004 survey of student experiences estimated that university students in the UK paid on average $54 per week in accommodation costs. Assume that this average is based on a sample 755 students and that the population standard deviation for weekly accommodation costs is $ 11. a. Construct a 90 per cent confi

Assessing Sample Size for the Number of "Walk-Ins"

Part of my job description is to teach Recruiters their daily individual tasks and how to properly manage their time. One of the Recruiter duties is to generate appointments in many different ways. They can visit high schools, Shopping Centers, or any other public places available within their Recruiting zone; their main goal

Confidence Interval

1. In each of the following exercises, a set of condition is given. To construct a 95 percent confidence interval for the population mean, would you use the z distribution, a t distribution, or neither? Where appropriate, determine the z or t value. n = 21, xbar = 23.1, s = 7.5, population distribution shape normal, σ = 7.

Confidence interval

A machine produces 9 inch latex gloves. A sample of 85 gloves is selected, and it is found that 36 are shorter than they should be. Find the 98% confidence interval on the proportion of all such gloves that are shorter than 9 inches

Find confidence interval

Use the given degree of confidence and sample data to find a confidence interval for the population standard deviation o. Assume that the population has a normal distribution. Weights of men: 90% confidence; n=14, Xbar=160.9lb, s=12.6lb


Week 8: ________________________________________ There are 2 pages in this exam. Be sure to complete all pages before submitting the exam. Page: 1 2 ________________________________________ Time Remaining: 1. (TCO 9) What is the feasible range for r, the correlation coefficient? (Points: 6) 0 to 1

Confidence Interval: Nursing school alumi & Auditor for bank

A nursing school wants to estimate the true mean annual income of its alumni. It randomly samples 200 of its alumi. The mean annual income was 55,200 with a standard deviation of 1,500. Find the 95% confidence inteval for the true mean annual income of the nursing school alumni. 2. An auditor wants to estimate what proporti


() is a pi symbol. 2. In the next presidential election of year 2012, five candidates running for the election are Sarah Palin, Hilary Clinton, Barack Obama, Mitt Romney, and Rudy Giuliani. It is desired to estimate the true proportion ( ) favoring one of the five candidates. a) based on sample size 1000 with 92% confidence,

Confidence Interval for ISO Certification

In a random sample of 100 manufacturing firms, 67 indicated that their company attained ISO certification within the last two years. Find a 95% confidence interval for the population proportion of companies that have been certified within the last two years. In solving the above question you must write the formula of the confide

Confidence intervals

1) A random sample, size 50, is taken from a large population, measuring the time it takes to complete a race. The sample mean is 44 minutes, the sample standard deviation 6.7 minutes. Calculate a 95% confidence interval around the sample mean 2) Do you use the z or t value? What value is used? 3) Interpret the conf


Statistics 2 1) Northeastern University (NU) wants to determine if its students spend more time studying than do students attending Boston University (BU). Random samples of 9 students are taken at BU and NU. The two samples reveal the following data: Daily hours studying at NU 6 3 0 3 6 0 2 3 4 Daily hours st

Statistics: finding correct z and t scores for confidence intervals

Finding appropriate z- and t-scores is important when constructing confidence intervals. Confidence intervals allow one to estimate important population parameters such as population mean, population proportion, population standard deviation, etc. We will also study how confidence intervals will let one determine how large of

SPSS Confidence Intervals and Chi-Squared: Example Problems

Assume you are the manager of a mustard seed factory in Colombia. Your company has received complaints that there is not enough mustard seed in your economy size packages. You ask your supervisor and chief operating officer Juan Valdez to test the new mustard seed packaging machine you are installing. He runs a sample of 36 pac

Confidence Interval estimation and interpretation.

Of 43 bank customers depositing a check, 18 received some cash back. (a) Construct a 90% confidence interval for the proportion of all depositors who ask for cash back. (b) Check the normality assumption.

Statistics Confidence Intervals for color of M&M candies

See attached files. Confidence intervals for the proportion of each color as well as the mean total number of candies per bag. You will use the methods of 6.3 for the proportions and 6.1 for the mean. For the Bonus, you will use the sample size formula on page 338. Please keep at least 4-6 decimal places for the sample pro

Statistics: Degrees of freedom, sampling error, interval estimate

1. A researcher conducts a two tailed two sample t test on 28 subjects (14 subjects in each Group) and finds that t=1.986. a. How many degrees of freedom are there in this study? b. Estimate the actual type 1 error for this study. c. If the researcher decides to reject the null hypothesis, how confident can the researche

Construction of confidence intervals and proper interpretation

Confidence Intervals: A confidence interval is simply a finite interval of score values on the dependent variable. Such an interval is constructed by adding a specific amount to the computed statistic (thereby obtaining the upper limit of the interval) and by the subtracting a specific amount from the statistic (thereby obtainin

Confidence interval for proportion

A large supermarket conducted a consumer preference study by recording the brand of wheat bread pruchased by customers in its stores. The supermarket carries four brands of wheat bread and the brand preferences of a random sample of 200 purchasers are given in the following table: BRAND A=51 B=82 C=27 D=40 Test the null

Statistics: Confidence Intervals

Confidence intervals are used to help you get a better feel for your estimated value. Confidence intervals are like nets. You don't know what the TRUE proportion value is so you throw a net (find a confidence interval based upon a survey). The confidence level indicates the percentage of times your net would "catch" the true pop

Determining 95% Confidence Interval and Mean

Julie is an industrial psychologist. She is currently studying stress among executives of health corporations. She developed a survey that he believes measures stress. A score of 80 indicates dangerous stress. A random sample of 15 executives revealed the following stress scores. Score 94 78 83 90 78 99 97 90 97 98

Confidence Interval

The quality control manager at a light bulb factory needs to estimate the mean life of a large shipment of light bulbs. The standard deviation is 100 hours. A random sample of 64 light bulbs indicated a sample mean life of 350 hours. A. Construct a 95% confidence interval estimate of population mean life of light bulbs in thi

Statistics: mean, median, deviation, histogram, binomial distribution, Poisson

1. Calculate the mean, median and standard deviation of the following data: 10, 16, 12, 20, 18, 209, 16, 11, 13, 14, 17, 20, 25 2. Prepare a relative frequency histogram of the following data, use 4 classes. 43, 35, 41, 41, 39, 38, 41, 40, 45, 43, 52, 36, 43, 38, 39, 44, 45, 30, 37, 40, 39, 41, 44, 46, 39, 40, 44, 37, 4

Random sample

1. The mean replacement time for a random sample of 12 microwave ovens is 8.6 years with a standard deviation of 4.2 years. Construct a 98% confidence interval for the population variance o^2. Assume the data are normally distributed. A. (7.8,63.6) B. (1.9,15.1) C. (2.8,8.0) d. (7.4,54.3) 2. The dean of a major university

Confidence Interval for Conusmer Purchase Amounts

Purchase Amounts for all Customers Shopping at a Local Supermarket on a Given Friday 4. Data of the amount that customers spend in a supermarket on a specific Friday. Assume this data represents the population. (20 points) a. What sample size would be required to be 95% sure that the estimate is within + $10? b. How woul

Hypothesis testing and conclusions

1. A machine produces 3-inch nails. A sample of 10 nails was selected and the lengths determined. The results are as follows: 2.89 2.95 3.00 3.05 2.99 2.96 3.10 3.06 3.00 3.12 Use these results to test H0:  = 3 and Ha:   3 at  = 0.01. Give the criti

Solving a Margin of Error Problem

The director of admissions has had questions from potential freshmen regarding the average price of textbooks per semester. In order to make an informed estimate of this cost, he selected a sample of 100 students and recorded their text book expenses for the most recent semester. He found a sample mean of $391.52. He assumes th


1. Out of a sample of 459 randomly selected light bulbs tested in a laboratory, 291 lasted more than 500 hours. a. Find a 90% confidence interval for the true population proportion of light bulbs that will last more than 500 hours. (5 points) b. Find a 95% confidence interval for the true population proportion of lig