Bias

Instructions

Start a fresh page in your classwork notebook. Write today’s date in the margin of the page. Clearly label and solve each of the following. Show your work and circle the anwer.

Discussion Questions

1. 2012, Practice Exam, #12

In the design of a survey, which of the following best explains how to minimize response bias?

1. Increase the sample size.

2. Decrease the sample size.

3. Randomly select the sample.

4. Increase the number of questions in the survey.

5. Carefully word and field-test survey questions.

2 . 2012, Practice Exam #15

A polling firm is interested in surveying a representative sample of registered voters in the United States. The firm has automated its sampling so that random phone numbers within the United States are called. Each time a number is called, the procedure below is followed.

• If there is no response or if an answering machine is reached, another number is automatically called.

• If a person answers, a survey worker verifies that the person is at least 18 years of age.

• If the person is not at least 18 years of age, no response is recorded, and another number is called.

• If the person is at least 18 years of age, that person is surveyed.

Some people claim the procedure being used does not permit the results to be extended to all registered voters. Which of the following is NOT a legitimate concern about the procedure being used?

1. Registered voters with children under the age of 18 years may be underrepresented in the sample.

2. Registered voters with unlisted telephone numbers may be underrepresented in the sample.

3. Registered voters who have more than one telephone number may be overrepresented in the sample.

4. Registered voters who live in households consisting of more than one voter may be underrepresented.

5. People who are not registered to vote may bias the sample results.

3. 2008, Free Response, #2

A local school board plans to conduct a survey of parents’ opinions about year-round schooling in elementary schools. The school board obtains a list of all families in the district with at least one child in an elementary school and sends the survey to a random sample of 500 of the families. The survey question is provided below.

A proposal has been submitted that would require students in elementary schools to attend school on a year- round basis. Do you support this proposal? (Yes or No)

The school board received responses from 98 of the families, with 76 of the responses indicating support for year-round schools. Based on this outcome, the local school board concludes that most of the families with at least one child in elementary school prefer year-round schooling.

1. What is a possible consequence of nonresponse bias for interpreting the results of this survey?

2. Someone advised the local school board to take an additional random sample of 500 families and to use the combined results to make their decision. Would this be a suitable solution to the issue raised in part a ? Explain.

3. Suggest a different follow-up step from the one suggested in part (b) that the local school board could take to address the issue raised in part a.

4. 2009, Free Response, #3

Before beginning a unit on frog anatomy, a seventh-grade biology teacher gives each of the 24 students in the class a pretest to assess their knowledge of frog anatomy. The teacher wants to compare the effectiveness of an instructional program in which students physically dissect frogs with the effectiveness of a different program in which students use computer software that only simulates the dissection of a frog. After completing one of the two programs, students will be given a posttest to assess their knowledge of frog anatomy. The teacher will then analyze the changes in the test scores (score on posttest minus score on pretest).

1. Describe a method for assigning the 24 students to two groups of equal size that allows for a statistically valid comparison of the two instructional programs.

2. Suppose the teacher decided to allow the students in the class to select which instructional program on frog anatomy (physical dissection or computer simulation) they prefer to take, and 11 students choose actual dissection and 13 students choose computer simulation. How might that self-selection process jeopardize a statistically valid comparison of the changes in the test scores (score on posttest minus score on pretest) for the two instructional programs? Provide a specific example to support your answer.