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Confidence Interval


Consumer products companies design different promotional activities to accomplish different goals. According to a spokesperson for General Mills, the company's cents-off coupon offers are designed to convince people to buy its products, while its refund offers (money returned with proof of repeated purchases) are designed to en

The importance of point estimates & confidence intervals

In our real world, where the quality and quantity of information ranges from excellent to terrible, would some measure of the certainty of the data tend to lead to better decisions? Can point estimates and confidence intervals help to provide some measure as to the certainty of data values?

Finding the Margin of Error and Confidence Level

I need to find out how to calculate the margin of error when given the data: c=95; s=0.10; n=20; x(bar) = 1.5 and how to construct a confidence interval of the population mean. This example is similar to my studies.

Estimating Population Values and confidence interval

The corporate operations manager for the Phillips Oil Company has his staff working on a new service-station layout plan that would potentially alter the ratio of regular unleaded pumps to other gasoline pumps (premium, super premium, etc) that are placed at a station. As part of the staff's analysis, they are interested in

Estimating Population Values

The AIMS Investment Company is interested in estimating the average number of mutual funds its customers have in their portfolios. a. based on the sample data, construct a 90% confidence interval estimate for the mean number of mutual funds for all their customers. Interpret this interval. b. Suppose that the interval est

Estimating Population Values

7.14 The First National bank is considering a survey of its customers to estimate the man number of checks written per month. A sample of 360 customers was selected. The sample values were _ X = 33.4 S = 11.2 a. Provide a 90% confidence interval e

Confidence Interval Calculations

Assume you are a tire manufacturer and want to determine what the tread life of a new line of tires is. A sample of 100 tires are run to failure and the average mileage is computed to be 55,000 miles with a standard deviation of 1000 miles. Compute the 95% confidence interval on the population mean. Interpret the interval. W

Statistics Multiple Choice

1. 1,600 of 2,000 voters say they plan to vote Republican. Use 0.95 degree of confidence to find the popltn proportion interval. A. 69.2 to 86.4% B. 76.5 to 83.5% C. 77.7 to 82.3% D. 78.2 to 81.8% E. none of the above 2. The mean weight of trucks traveling on the the highway is unknown. A state highway inspec

Develop a 95% confidence interval estimate for the mean of the population

1. An printout of the descriptive measures of daily checking account balances (in $) of bank customers is shown below. Develop a 95% confidence interval estimate for the mean of the population of the checking balances. Account Balance Information Mean 4828.29 Median 5115.25 Mode 4976.50 Standard Deviation 1143.57 Sampl

Statistics: Comparisons Involving Means and confidence interval

FedEx and United Parcel Service (UPS) are the world's two leading cargo carriers by volume and revenue. According to the Airports Council International, the Memphis International Airport (FedEx) and the Louisville International Airport (UPS) are two of the ten largest cargo airports in the world. The following random samples (in

Values for confidence intervals

Find the z and t values for the follow confidence intervals. Note that sample size does not apply for a z value. Compare the z value for 95% with the two t values for 95%. . All the confidence levels are the same. Comment on the z and t values; are they different? Why, do you think?

Confidence Intervals and Margin of Error

Need assistance setting up and solving this problem: The National Center for Education Statistics reported that 47% of college students work to pay for tuition and living expenses. Assume that a sample of 450 college students was used in the study. a. Provide a 95% confidence interval for the population proportion of colleg

Number of Respondents Required

In a public opinion poll 48% of 189 respondents favor an elimination of taxes on dividend income. How many respondents would be needed to calculate a 95% confidence interval (for the proportion of people who favor an elimination of taxes on dividend income) that has a total width no greater than 4% (the estimate must be within +

Statistics - 95% error margin and 98% confidence interval

1. A company wishing to improve its customer service collected hold times from 75 randomly selected incoming calls to its hot line that were put on hold. These calls had sample mean hold time = 3.4 minutes and s = 2.3 minutes. Is the claim that μ > 3.0 minutes substantiated by these data? Test with α = .05. 8.95

95% confidence interval - statistics

Hack Wilson¿s major league record of 190 runs batted in during a single season in professional baseball has stood for 70 years. Perhaps the reason for this longevity is that the average for all the other league leaders is so far below the total Wilson knocked in back in 1930. A confidence interval might provide a clue. A random

Statistics - 95% confidence intervals

The following table shows the mean daily average temperature in San Diego, California for each of the 12 months of the year: Month Jan Feb Mar Apr Nay June July Aug Sep Oct Nov Dec °F 54.9 55.9 57.6 59.9 62.2 65.1 68.7 70.2 68.5 64.8 60.1 56.1 Construct a 95% confidence interval for the mean annual temperature in San D

Applying statistics to a variety of situations

1. The time it takes for a taxi to drive from the office to the airport was recorded on 40 occasions. It was found that minutes and s = 5 minutes. Give (a) An estimate of ì = population mean time to drive. (b)An approximate 95.4% error margin. 2 On a Thursday, students were asked to report the number of hours sleep t

Confidence Intervals

Calculate and interpret 90%, 95%, and 99% confidence intervals for both groups of approaches. Also provide 90%, 95%, and 99% confidence intervals for both groups when the sample size is increased from 10 to 50. Interpret all statistics Group 1: rational-emotive approach scores: 56, 42, 38, 41, 42, 25, 66, 38, 55, 61 Group

Mean Score Confidence Interval for a Mental Health Questionnaire

A nursing professional conducts an analysis to examine scores on the mental health service and treatment outcome questionnaire. A sample of 16 patients gives the following summary statistics for one item addressing health problems: N Mean S 16 907.75 8.4814 Give a 95% confidence interval for the mean score.

Sample Size for Criminology

A criminology professor has been teaching graduate and undergraduate statistics for a few years. Her records show that the overall mean for final exam scores is 82 with a standard deviation of 10. The professor believes that this year's class is superior to her previous classes. She decides to conduct a test on the 25 students

Statistics Problem: Confidence Interval

A sample of 30 patients was studied in an effort to assess agency' preparedness for delivery of mental health services to African Americans. A nursing researcher and counselor decided to collaborate and conduct the study using the Clinical Attitudes, Knowledge, and Skills Inventory (CAKSI) to assess preparedness for delivery of

Confidence interval for the population mean: Use of the t distribution

Could you provide the excel spreadsheet so that I can input #s and find the lower limit and upper limit of the confidence interval. A sample question is: Suppose that a random sample of eleven recently sold houses in a certain city has mean sales price of $290,000, with a standard deviation of $7,000. Under the assumption

Confidence Interval of the Mean

A quick study found that the average time it took a person to find a new job was 5.9 months. If a sample of 36 job seekers was surveyed, find the 95% confidence interval of the mean. Assume the standard deviation is .8 months, and how would you explain this to a layperson?

Confidence Interval of Automobile Shop Managers

An automobile shop manager timed six employees and found the average time it took then to change a water pump was 18 minutes. The standard deviation of the sample was 3 minutes. Find the 99% confidence interval of the true mean, and how would you explain the interval to the average layperson

Hypothesis Testting, Confidence Intervals and Levels of Significance

In a statistics lecture, students are asked whether or not they enjoyed doing statistics. Random sample of 50 students was taken and 30 of them said that they enjoyed doing statistics. The lecturer claimed that more than 50% of the students enjoyed doing statistics. (i) Test, at the 5% level of significance, whether or not

Confidence Intervals and Standard Deviation

In a manufacturing process, the diameter of the steel rods is the product characteristic. A random sample of 25 steel rods is taken and sample mean is 8.88 cm. The diameter is assumed to be normally distributed with standard deviation 1.25. (i) Find a 95% confidence interval for the true diameter. If the standard deviation

Confidence Interval

A random sample of 172 students was asked to rate on a scale to from 1 (not important) to 5 (extremely important) health benefits as a job characteristic (note that the rating scale can also have decimals, i.e. a student can give a rating of 1.32). The sample mean rating was 3.31, and the sample standard deviation was 0.70.

Confidence Interval

What is meant by confidence interval? Please explain with real life examples.