Share
Explore BrainMass

Confidence Interval

Calculation of Confidence Interval for Population Proportion

A random sample of 600 registered voters yields 360 in favor of the slow growth initiative. a. Compute the 99% confidence interval for the percentage of registered voters who favor the slow growth initiative. Interpret this interval. b. How many registered voters should be sampled in order to be 99% confident of being with

Width of the confidence interval

Discuss what happens to the width of the confidence interval as the sample size is decreased. Discuss what happens to the width of the confidence interval as the confidence level is increased. Is this reasonable? Explain.

Confidence Interval and Sample Size Determination

Families USA, a monthly magazine that discusses issues related to health and health costs, surveyed 20 of its subscribers. It found that the annual health insurance premiums for a family with coverage through an employer averaged $10,979. The standard deviation of the sample was $1,000. a. Based on this sample information, deve

Statistics

Biting an unpopped kernel of popcorn hurts! As an experiment, a self-confessed biting an unpopped kernel of popcorn hurts! As an experiment, a self-confessed connoisseur of cheap popcorn carefully counted 773 kernels and put them in a popper. After popping, the unpopped kernels were counted. There were 86. (a) Construct a 90 per

Forecasting

Forecasting is not to clear to me, how do I get started? Given the following data on hotel check-ins for a 6-month period: Month Number of rooms July 70 August 105 September 90 October 120 November 110 December 115 a. What is the 3-month moving average for January? b. What is the 5-month moving average for Jan

A) Determine the 95% confidence interval estimates of the mean medical costs for each of the four age categories. b) For each year listed, determine the 95% confidence interval estimates of the total medical costs for Canadians 45 years old and older.

12.3-question 1 A statistics practitioner has been given the task of making these predictions. Accordingly, random samples of four groups of Canadians were drawn. They are Group Ages 1 45-64 2 65-74 3 75-84 4 85 and over Age group 2011 2016 2021 2026 2031 45-64 9718 10013

Statistics - Confidence Interval .

Describe the confidence interval for the survey of 10,000 families who are potential home buyers for homes in the following price ranges: $130,000 - $200,000, $200,000 0 $250,000 and $250,000 - $350,000. This is a research to assist financial institutions and realtors find potential home buyers.

The Confidence Interval for the Population Mean

A random sample of 121 automobiles traveling on an interstate showed an average speed of 65 mph. From past information, it is known that the standard deviation of the population is 22 mph. Determine a 96.6% confidence interval for the mean.

Determining Margin of Error: Example Problem

A Gallup Poll of 1002 adults found that 25% of the respondents said that their household had experienced a crime in the past year. Among respondents aged 18 to 29 years, 43% had been victims of a crime. Gallup says, "For results based on the total sample of national adults, one can say with 95% confidence that the margin of samp

Speculations about a study result

This question is asking for speculation about the possible results of a study if we change the size of the population. It all depends on unknowns such as how representative the 100 adults are of the population. In general, the larger the population the more sure we are that it is representative of the population. In a poll o

99 percent confidence interval

1. A sample set of weights in pounds are 1.01, .95, 1.03, 1.04, .97, .97, .99, 1.01 and 1.03. Assume the population of weights are normally distributed. Find a 99 percent confidence interval for the mean population weight. 2. Based on a random sample of 25 units of product X, the average weight is 102 lbs. and the sample

Developing Percent Confidence Intervals

1. The success rate of a surgical procedure is 70 per 100 cases examined in a sample. Find a 90 percent confidence interval for the total number of successes per 1,000 cases. 2. Ten items of 100 are defective. Develop a 95 percent confidence interval for the population proportion of defectives. 3. Assuming a normal popul

95 percent confidence interval

Of a random sample of 600 trucks at a bridge, 114 had bad signal lights. Construct a 95 percent confidence interval for the percentage of trucks that had bad signal lights.

Determining a confidence interval

Computer Services, Inc., wants to determine a confidence interval for the average CPU time of their teleprocessing transactions. A sample of 64 transactions yielded a mean of 6 seconds with a standard deviation of 0.8 seconds. Determine a 98% confidence interval for the average CPU time.

Confidence interval for mean ..

A random sample of 81 credit sales in a department store showed an average sale of $68.00. Historically, it is known that the standard deviation of the population is $27.00. a) determine the standard error of the mean, b) with a 0.95 probability, what can be said about the margin of error and c) what is the 95% confidence interv

Confidence Intervals for a Population Mean

A random sample of 144 observations has a mean of 20, a median of 21 and a mode of 22. The population standard deviation is known to equal 4.8. What is the 95.44% confidence interval for the population mean?

Finding the Confidence Interval for Mean Number of Hours

5. A researcher wants to estimate the mean number of hours (mu) ; children watch television per day. A sample of 38 children is taken. The sample mean is 6.8 hours with a sample standard deviation of 1.1 hours. a. Find the 90% confidence interval for mean (mu). b. Find the 95% confidence interval for mean (mu).

Determining the confidence interval for the mean

4. The owner of a business wanted to test how long employees were spending on the internet. A random sample of 49 employees showed a mean of 42 minutes and a standard deviation of 5.2 minutes. Find a 90% confidence for the mean.

Confidence interval for mean

2. A physician wanted to estimate the mean length of time μ that a patient wanted to see him after arriving. A random sample of 64 patients showed a mean waiting time of 23.4 minutes and a standard deviation of 7.1 minutes. Find a 95% confidence interval for μ.

Confidence interval estimation and normal distribution

A laboratory tested eleven chickens and found that the mean amount of cholesterol was 244 milligrams with s = 24.92 milligrams. Construct a 95 percent confidence interval for the true mean cholesterol content of all such eggs. Assume that the population has a normal distribution.

Confidence interval estimation problem

1. A group of 47 randomly selected students have a mean score of 20.2 with a standard deviation of 4.6 on a placement test. Construct a 90% confidence interval for the mean score, , of all students taking the test.

Confidence Interval

A recent survey of 50 executives who were laid off from their previous position revealed it took a mean of 26 weeks for them to find another position. The standard deviation of the sample was 6.2 weeks. Construct a 95 percent confidence interval for the population mean. Is it reasonable that the population mean is 28 weeks?

Confidence Interval Estimation for Proportion

A local health center noted that in a sample of 400 patients 80 were referred to them by the local hospital. What size sample would be required to estimate the proportion of hospital referrals with a margin of error of 0.04 or less at 95% confidence?

Margin of error calculation

"In order to estimate the average time spent on the computer terminals per student at a local university, data were collected for a sample of 81 business students over a one week period. Assume the population standard deviation is 1.8 hours. With a 0.95 probability, the margin of error is approximately."

Confidence Interval

A researcher is interested in determining the average number of years employees of a company stay with the company. If past information shows a standard deviation of 7 months, what size sample should be taken so that at 95% confidence the margin of error will be 2 months or less?"

Confidence Interval for Time Spent on Computer Terminals

In order to estimate the average time spent on the computer terminals per student at a local university, data were collected for a sample of 81 business students over a one week period. Assume the population standard deviation is 1.8 hours. If the sample mean is 9 hours, then the 95% confidence interval is?

Hypothesis Testing and Confidence Interval Problems

1. Two teachers give the same standardized statistics test. The results are: Teacher 1 Mean=75 N=20 Teacher 2 Mean=80 N=15 a. What would be a 95% confidence interval for each of the classes? b. The true mean for the test is 70, with a standard deviation of 5. Can you draw any conclusions about either of the clas

Confidence interval and Normal distributions

In a class there are 60 students. The mean exam score is 70 and the standard deviation is 5. (Be Precise in your answers!) Assume symmetric distribution of the scores. (i) What can you say about the number of students that have scores between 55 and 85? (ii) What can you say about the number of students who ha

Estimation:

The management of a department store is interested in estimating the difference between the mean credit purchases of customers using the store's credit card versus those customers using a national major credit card. You are given the following information. Store's Card Major Credit Card Sample size 64 49 Sample mean $140 $1