Explore BrainMass

Confidence Interval

Understanding confidence intervals

What do we mean by confidence intervals - provide an example that illustrates your answer. Suppose we were to apply 95% and 99% confidence to your study results.. how might your result differ and why?

Calculations with confidence interval for mean

Please help with the following problems. 1. For df = 25, determine the value of A that corresponds to each of the following probabilities: a.P(t > A) = 0.25 b. P( < A) = 0.10 c. P(-A < t < A) = .99 2. Given the following observations in a simple random sample from a population that is approximately normally distrib

Confidence Interval for mean

An assembly process inlcudes a torque wrench device that automatically tightens compressor housing bolts; the device has a known process tandard deviation of o = 3 lb-ft in the torque applied. A simple random sample of 35 nuts is selected, and the average torque to which they have been tightened is 150 lb-ft. What is the 95%

Confidence intervals and means

The mean number of travel days per year for the outside salespeople employed by hardware distributors is to be estimated. The 0.90 degree of confidence is to be used. The mean of a small pilot study was 150 days, with a standard deviation of 14 days. If the population mean is to be estimated within two days, how many outside sal

Confidence Intervals and One-Sample Hypothesis Test

See attachment for fully formatted question. ----------------------------------------------------------------- Confidence Intervals and One-Sample Hypothesis Test 1. Collect data. Develop a 90% confidence interval and a 95% confidence interval for the population mean. Did you use a z statistic or t statistic? Why? Compare

Student Earnings: Confidence intervals and margins of error

6. Salaries: Student services consider college officials in admissions, registration, counseling, financial aid, campus ministry, food service, and so on. How much money do these people make each year? Suppose you read in your local newspaper that 45 officials in student services earned an average of = $50,340 each year. a

Sample Population Confidence Intervals Case Study

1. Collect data. Develop a 90% confidence interval and a 95% confidence interval for the population mean. Did you use a z statistic or t statistic? Why? Compare the size and meaning of the two confidence intervals. 2. Take a random sample and test a hypothesis about a population mean. Explain what assumptions you made.

Statistics - Hypothesis Test - Confidence Interval

Problem: A new product was test marketed in the Des Moines, Iowa, and Toledo, Ohio, metropolitan areas. Advertising in the Des Moines area was done entirely on television, while adverising in the Toledo area consisted of a mixture of television, radio, newspaper and magazine ads. Two months after the advertising campaigns com


Select the correct answer and write the appropriate letter in the space provided. ______ 1. A single number used to estimate a population parameter is a. the confidence interval. b. the population parameter. c. a point estimate. d. the mean of the population. ______ 2. A range of values constructed from sample data so

Use Excel to Construct Confidence Intervals

See the attached file. Please help in setting up and solving the problem given below. The problem with necessary data is fully set up in the attached Excel document. INSTRUCTION: Include a "summary statement" for each CI. Use the data for which is given in columns A:C. FACTS / PROBLEM: USE EXCEL AND EXCEL FUNCTIONS

Data Analysis - Finding Sample Sizes for Confidence Intervals

INSTRUCTIONS: Include a "summary statement" for each CI. FACTS: Elected officials in a small Florida town are preparing for the annual budget for their community. Specifically, they would like to estimate how much their constituents living in this town are typically paying each year in real estate taxes. Given that the

Confidence Interval and Mean Difference

The director of a university's development center is interested in comparing the starting annual salaries of male and female students who recently graduated form the university and commenced full-time employment. The director has formed pairs of male and female graduates with the same major and similar grade point averages. Sp

Confidence Interval, P-Value & Hypothesis Testing

See the attached file. Problem 1: A bank in a small town has 10,000 customers. A national survey on the banking habits of people in U.S. shows that 80% of the people with income higher than 50,000 dollars have both savings and checking accounts and also shows that the average number of banking operations that a person aged 18

Statistics: Confidence Intervals and Significance Levels

Please see the attached file for the fully formatted problems. Assignment 2: Mixed Problems 1. In your own words explain the difference between a point estimate and an interval estimate of a parameter? Which is better? Why? Answer: The point estimate is the value that is specific and is a single number of a paramete

Inference from Two Samples: hypothesis tests and confidence intervals.

Heights of Winners and Runners-Up Listed below are the heights of candidates who won presidential elections and the heights of the candidates with the next highest number of popular votes. The data are in chronological order, so the corresponding heights from the two lists are matched. For candidates who won more than once, o

Confidence Intervals of the Difference Between Population Means

In these two exercises, assume that the two samples are independent random samples selected from normally distributed populations. Do not assume that the population standard deviations are equal, unless stipulates otherwise. The Confidence Interval for Comparing Diets A randomized trial tested the effectiveness of diets o

A consumer magazine has contracted a simple random sample of 33 owners of a certain model of automat bile and asked each owner how many defects had to be corrected within the first 2 months of owners

A consumer magazine has contracted a simple random sample of 33 owners of a certain model of automat bile and asked each owner how many defects had to be corrected within the first 2 months of ownership. The average number of defect was x-bar = 3.7, with a standard deviation of 1.8 defects. a. Use the t distribution to constru

Finding Confidence Intervals

Minting Quarters Quarters are currently minted with weights having a mean of 5.760 g and a standard deviation of 0.062 g. New equipment is being tested in an attempt to improve quality by reducing variation. A simple random sample of 24 quarters is obtained from those manufactured with the new equipment, and this sample has a

Shoveling Heart Rates. Find and interpret confidence intervals for the mean.

Shoveling Heart Rates Because cardiac deaths appear to increase after heavy snowfalls, an experiment was designed to compare cardiac demands of snow shoveling to those of using an electric snow thrower. Ten subjects cleared tracts of snow using both methods, and their maximum heart rates (beat per minute) were recorded during

Test Tires Using a 95% Confidence Interval of Average Mileage

"Joe" is he shop manager at a truck line and is approached by a salesman about some new tires. The salesman assures Joe that the tires will get an average of 60,000 miles before wearing out. Not being that gullible Joe asks for 100 tires for a test. The tires are mounted and run to wear-out and the 95% confidence interval of

Confidence Intervals, Sample Size, and Confidence Levels

1. Can you give a general rule as to what happens with confidence intervals as a function of sample sizes and confidence levels? What are the trade-offs? 2. Take a sample of something in your work environment, something simple, and calculate a confidence interval. Some possible samples: the average number of people in y

T Critical and Confidence Interval

See the attached file. 2) Use Table 4 of the appendix to find tc for a 0.99 confidence level when the sample size is 4. 4) Use Table 4 of the Appendix to find tc for 0.95 confidence level when the sample size is 12. 6) Wildlife: Wolf Pups. The number of pups in the wolf dens of the southwestern United States is recorded b

Confidence Intervals and Statistics Testings

1. The P-value for a two sided test of the null hypothesis H0: µ = 30 is 0.04. a) Does the 95% confidence interval include the value 30? Why? b) Does the 90% confidence interval include the value 30? Why? 2. The level of calcium in the blood in healthy young adults varies with mean about 9.5 milligrams per deciliter and st

Exercises of Applied Statistics in Business and Economics

Please complete these 2 exercises from Applied Statistics in Business and Economics. 8.46 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 conf

Confidence interval calculation

1. A quality engineer is responsible for maintaining control of the bottling process in a beer factory. The goals is to maintain the intended volume (6 oz) with as little variation as possible. Since product sampled is not suitable for sale and becomes waste, it is very important to sample a minimal number of bottles. However, i