# Explain the difference between bias and variability in sampling results

 Date 19.05.2016 Size 47.13 Kb.

 1 A polling company working for a candidate for governor surveys a sample of 2500 registered voters in the state to determine if they are in agreement with the candidate's stand on gun control. Describe the population for this study.

 2 A biologist draws a sample of 200 fish from a lake to test for mercury levels. She finds that 8% have levels above limits set as healthy. Describe the population for this study.

 3 In order to determine if students on a college campus are in favor of a tuition hike to pay for expanded parking services, a member of the student senate surveys 25 people in a commuter parking lot. Why is this a poor sampling technique?

 4 Convenience samples are said to be highly likely to produce bias in survey results. Explain why this is true.

 5 Explain the difference between bias and variability in sampling results.

 6 We wish to know what proportion of students at a major university believe too much emphasis is placed on athletics at the school. Explain how we could choose a sample of 500 students to reduce the possibility of bias in the results.

 7 In order to determine what proportion of a town's residents approve of a new plan for trash collection, the town council placed an ad in the newspaper asking residents to phone in their opinions. Explain why the results of this poll may differ from the actual beliefs of all residents in the town.

 8 Define a simple random sample.

 9 Can we eliminate variability in results of sampling? Why or why not?

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Use the random digits table, beginning at line 103, to choose a sample of four people from the following list:

 01 Adams 06 Ford 11 Kramer 16 Post 02 Brown 07 Goodman 12 Loomis 17 Quayle 03 Cook 08 Harris 13 Martin 18 Rogers 04 Davis 09 Inez 14 Norton 19 Stevens 05 Elliot 10 Jones 15 O'Hare 20 Thompson

 11 We must use a random digits table to choose a sample of eight names from the roster of a club with 100 members. Why can we use two-digit numbers from the table to select our sample?

 12 The marketing department of a large national corporation wishes to determine what proportion of the residents of a state may be interested in buying its new product. Describe how the corporation might use a multi-stage random sampling process to choose a sample of the state's residents to survey.

 13 A high school principal wishes to determine what proportion of the school's students like the new school mascot. The principal decides to survey every 25th name from the school enrollment records (an alphabetical list of all students at the school). Is this a valid simple random sampling technique? Why or why not?

 14 In a poll of 2500 residents of a state it is found that 480 are in favor of naming the grasshopper the state insect. What is the sample proportion for this poll?

 15 A marketing department surveys 1500 shoppers and finds that 950 would visit a new store more often if were open Sunday evenings. What is the sample proportion in this survey?

 16 Why do opinion polls usually report a "margin of error" with the results of a survey? What does the margin of error mean?

 17 What is the difference between an observational study and an experiment?

 18 One July, the city council of a small town decides to impose an experimental curfew on all residents under 18 to cut down on loitering in the town square. After four months, the number of teens found in the square after dark has decreased 80%, and the council declares the curfew a success. Explain why this conclusion may not be valid.

 19 A farmer believes that exposing chickens to classical music will cause them to produce more eggs. Describe how the farmer may design a randomized comparative experiment to test this theory.

 20 A school superintendent believes a new approach to teaching children to read will produce better standardized test scores in the district. Describe how the superintendent may design a randomized comparative experiment to test this theory.

 21 A school principal is concerned with the increasing level of absenteeism in the school. A meeting of parents, teachers, and students is called at which the principal expresses her concern and describes an experimental program that will be instituted to try to curb absenteeism. After two months, absenteeism is down by 15%. Explain how confounding variables may have affected the results of the experiment.

 22 Medical experiments are frequently double blind. Explain what this means and why medical experiments are designed this way.

 23 Describe what is meant by the placebo effect in an experiment.

 24 How does a randomized comparative experiment control the effects of confounding variables?

 25 What does it mean to say that the results of an experiment are statistically significant?

 26 Officials at a university want to determine the percentage of students who favor the allocation of a percentage of tuition funds toward the construction of a new campus parking garage. To find this out, a survey is conducted. One thousand people driving through the administration building parking lot are surveyed, and it is found that 75% of these people favor the garage. Explain why this conclusion might not be valid.

 27 Officials at a university want to determine the percentage of students who favor the allocation of a percentage of tuition funds toward the construction of a new campus parking garage. To find this out, a survey is conducted. One thousand people driving through the administration building parking lot are surveyed, and it is found that 75% of these people favor the garage. What is the population in this study? What is the sample?

 28 A new stadium is being planned for the local professional football team. One of the proposed funding methods involves the allocation of tax monies to build the stadium. To determine the public opinion of this plan, the first 100 people entering the stadium for a game are surveyed. Explain why the results of this survey might not be valid.

 29 A recent survey of 536 employees of U.S. corporations determined that 84% of them feel that the executives who run their companies are ethical. Determine the 95% confidence interval for this survey.

 30 A survey of 127 patients in a particular hospital determined that 54% of them felt that they were receiving excellent care. Determine the 95% confidence interval for this survey.