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Confidence Interval

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 Quality Control Managers

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

Descriptive Statistics, Probability & Confidence Interval

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

Statistics

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

Using and Interpreting Concepts

An election poll reported that a candidate had an approval rating of 48% with a margin of error E of 3%. Construct a confidence interval for the proportion of adults who approve of the candidate. You are a travel agent and wish to estimate, with 95% confidence, the proportion of vacationers who plan to travel outside the Unit

Population Proportion, Estimation and Confidence Levels

As a condition of employment, Fashion Industries applicants must pass a drug test. Of the last 220 applicants 14 failed the test. Develop a 99 percent confidence interval for the proportion of applicants that fail the test. Would it be reasonable to conclude that more than 10 percent of the applicants are now failing the test? I

Confidence interval and t-distributions

In a random sample of 62 bolts, the mean length was 1.87 inches and the standard deviation was 0.07 inch. Use a normal distribution or a t-distribution to construct a 90% confidence interval or the mean. Which distribution should be used to construct the 90% confidence interval? A. Use a normal distribution because the len

Confidence Interval for Election Polls

An election poll reported that a candidate had an approval rating of 30% with a margin of error E of 4%. Construct a confidence interval for the proportion of the adults who approve of the candidate. The confidence interval for the proportion of adults who approve of the candidate is ( , ). round to two decimal places as

Confidence Interval for Population Mean

In a random sample of six microwave ovens, the mean repair cost was $90.00 and the standard deviation was $11.00. Assume the variable is normally distributed and use a t-distribution to construct a 90% confidence interval for the population mean u. What is the margin of error of u? The 90% confidence interval for the popula

11 Probability questions

Find the indicated probability or percentage for the normally distributed variable. 1) The variable X is normally distributed.The mean is &#956; = 22.0 and the standard deviation is &#56256;&#57239; = 2.4. 1) Find P(19.7 < X < 25.3). A) 0.4107 B) 1.0847 C) 0.3370 D) 0.7477 2) The incomes of trainees at a local mill are n

Confidence interval for mean ..

Confidence Intervals for the Mean (Small Samples) An experimental egg farm is raising chickens to produce low cholesterol eggs. A lab tested 16 randomly selected eggs and found that the mean amount of cholesterol was X(with line above the X) = 190 mg. The sample standard deviation was found to be s = 18.0 mg on this group

Confidence interval for population proportion

Confidence Intervals for Population Proportions 5.The new Twinkle bulb is being developed to last more than 1000 hours. A random sample of 100 of these new bulbs is selected from the production line. It was found that 64 lasted more than 1000 hours. Find the point estimate for the population proportion, the margin of error fo

Levels of Confidence and Intervals

1. Find the level of confidence assigned to an interval estimate of the mean formed using the interval: x − 1.96⋅σx to x + 1.96⋅σ x . 2. The lengths of 225 fish caught in Lake Michigan had a mean of 15.0 inches. Assume that the population standard deviation is 2.5 inches. - Give a point estimate for μ . - F

Using the data given, find the time of day that has the shortest commute time.

I need to measure minutes to and from work versus the time of day I leave. The objective is to find the time of the day that takes the least amount of time to get to work from the data given. I would like the results to include a bell curve if possible. What would be the best form of measure: linear regression or null hypot

Families USA Confidence Interval

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