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Ashford 5: - Week 4 (May 12 - May 18)

Overview

Assignment	Due Date	Format	Grading Percent
Confidence Intervals	Day 3 (1st post)	Discussion	3
Chi-Square Tests	Day 3 (1st post)	Discussion	3
Week Four Quiz	Day 6	Quiz	5
Problem Set Week Four	Day 7	Assignment	8

Note: The online classroom is designed to time students out after 90 minutes of inactivity. Because of this, we strongly suggest that you compose your work in a word processing program and copy and paste it into the discussion post when you are ready to submit it.

Learning Outcomes This week students will:

1. Interpret confidence intervals for t-tests.

2. Explain how standard deviations in variables affect confidence intervals.

3. Draw conclusions from interval data.

Introduction

For Week Four, students will focus on confidence intervals as useful indicators of population characteristics. This is important given that it will provide what is otherwise unknown and inaccessible. In Chapter 12, students will be introduced to chi-square tests. This is a test used to compare observed frequencies. When only one set of frequencies is examined, this is often called a goodness-of-fit test and is used to determine whether the observed frequencies fit within the range that would be expected.

Required Resources Required Text

1. Read the following chapters from Statistics for Managers:

a. Chapter 11: Confidence Intervals Note: You do not need to read Section 11.3

b. Chapter 12: The Chi-Square Test: Analyzing Categorical Data

Recommended Resources Multimedia

1. Khan Academy. (Producer). Inferential statistics [Video files]. Retrieved from https://www.khanacademy.org/math/probability/statistics-inferential.

2. Meridian Education Corporation & MotionMasters, Inc. (Producers). (2010). Deadly driving distractions: Texting, cell phones, and other killers [Video File]. Retrieved from the Films On Demand database.

Discussions To participate in the following discussions, go to this week's Discussion link in the left navigation.

1. Confidence Intervals Many people do not “like” or “trust” single point estimates for things they need measured. Looking back at the data examples you have provided in the previous discussion questions on this issue, how might adding confidence intervals help managers accept the results better? Why? Ask a manager in your organization if they would prefer a single point estimate or a range for important measures, and why? Please share what they say. Guided Response: Review several of your classmates’ posts. Respond to at least two classmates by commenting on whether or not you think adding or using confidence intervals would result in greater acceptance. Explain if you agree or disagree with the role of a confidence interval in the interpretation of the answer.

2. Chi-Square Tests Chi-square tests are great to show if distributions differ or if two variables interact in producing outcomes. What are some examples of variables that you might want to check using the chi-square tests? What would these results tell you? Guided Response: Review several of your classmates’ posts. Respond to at least two classmates by commenting on how this information might be used to make business decisions..

Quiz To complete the following quiz, go to this week's Quiz link in the left navigation.

Week Four Quiz This quiz consists of 10 questions. The amount of time the quiz will take to complete will vary by individual.

Assignment To complete the following assignment, go to this week's Assignment link in the left navigation.

Problem Set Week Four Let’s look at some other factors that might influence pay. Complete the problems included in the resources below and submit your work in an Excel document. Be sure to show all of your work and clearly label all calculations. All statistical calculations will use the Employee Salary Data Set and the Week 4 assignment sheet.

Carefully review the Grading Rubric for the criteria that will be used to evaluate your assignment.

Ashford 5: - Week 4 - Instructor Guidance

Week Four Guidance

Weekly Overview

Background

Suffolk Home Center distributes home improvement in the northeastern United States. As a company accountant, you are responsible for the accuracy of the integrated inventory management and sales information system. You can review the contents of each and every record to check the accuracy of this system, but such a detailed review would be time-consuming and costly. A better approach is to use statistical inference techniques to draw conclusions about the population of all records from a relatively small sample collected during an audit. At the end of each month, you could select a sample of the sales invoice to estimate the following:

1. The mean dollar amount listed on the sales invoices for the month

2. The proportion of invoices that contain errors that violate the internal control policy of the warehouse.

How accurate are the results from the samples and how do you use this information? Are the sample sizes large enough to give you the information you need?

In this week, you learn:

o To construct and interpret confidence interval estimates for the mean and the proportion

o How to determine the sample size necessary to develop a confidence interval for the mean or proportion

Confidence Interval Estimate

A confidence interval estimate is a range of numbers, called an interval, constructed around the point estimate. The confidence interval is constructed such that the probability that the population parameter is located somewhere within the interval is known.

An interval gives a range of values:

 Takes into consideration variation in sample statistics from sample to sample

 Based on observations from 1 sample

 Gives information about closeness to unknown population parameters

 Stated in terms of level of confidence, e.g. 95% confident, 99% confident,

 Can never be 100% confident

Interpretation Example

We are 95% confident that the true mean resistance is between 1.9932 and 2.4068 ohms

Although the true mean may or may not be in this interval, 95% of intervals formed in this manner will contain the true mean.

Chi-Squre Tests

Background

You are the manager of Lei Resort Properties, a collection of five upscale hotels located on two tropical islands. Guests who are satisfied with the quality of services during their stay are more likely to return on a future vacation and to recommend the hotel to friends and relatives. To assess the quality of services being provided by your hotels, guests are encouraged to complete a satisfaction survey when they check out. You need to analyze the data from these surveys to determine the overall satisfaction with the services provided, the likelihood that the guests will return to the hotel. And the reasons some guests indicated that they will not return. For example, on one island, Lei Resort Properties operates the Beachsand and Lakeview hotels. Is the perceived quality at the Beachsand Hotel the same as at the Lakeview Hotel?

Chi-squre test is for analyzing categorical response data from two or more samples

Contingency Tables

 Useful in situations involving multiple population proportions

 Used to classify sample observations according to two or more characteristics

 Also called a cross-classification table.

Discussion

You need to understand the use of confidence interval and Chi-squre test.

Assignment

#1 and #2 A similar example of the confidence interval is in chapter 11.1, p 287. You need mean and standard deviation to calculate confidence intervals.

3. An similar example of the Chi-squire test is in chapter 12.5, p 320. You need to enter data before using Excel to conduct the test (I entered the first raw, you need to continue).

You need to calculate value of Chi-square and p –value, and then interpret the results

4. This is similar to #3…it’s a Chi-square test.

Ashford 5: - Week 4 - Discussion 1

Your initial discussion thread is due on Day 3 (Thursday) and you have until Day 7 (Monday) to respond to your classmates. Your grade will reflect both the quality of your initial post and the depth of your responses. Reference the Discussion Forum Grading Rubric for guidance on how your discussion will be evaluated.

Confidence Intervals

Many people do not “like” or “trust” single point estimates for things they need measured. Looking back at the data examples you have provided in the previous discussion questions on this issue, how might adding confidence intervals help managers accept the results better? Why?

Ask a manger in your organization if they would prefer a single point estimate or a range for important measures, and why? Please share what they say. Guided Response: Review several of your classmates’ posts. Respond to at least two classmates by commenting on whether or not you think adding or using confidence intervals would result in greater acceptance. Explain if you agree or disagree with the role of a confidence interval in the interpretation of the answer.

Ashford 5: - Week 4 - Discussion 2

Chi-Square Tests

Chi-square tests are great to show if distributions differ or if two variables interact in producing outcomes. What are some examples of variables that you might want to check using the chi-square tests? What would these results tell you? Guided Response: Review several of your classmates’ posts. Respond to at least two classmates by commenting on how this information might be used to make business decisions.

Ashford 5: - Week 4 - Assignment

Problem Set Week Four Let’s look at some other factors that might influence pay. Complete the problems included in the resources below and submit your work in an Excel document. Be sure to show all of your work and clearly label all calculations. All statistical calculations will use the Employee Salary Data Set and the Week 4 assignment sheet.

Carefully review the Grading Rubric for the criteria that will be used to evaluate your assignment.