Bias and Unbiased Sample

When a sample does not accurately represent the population it is a:

• Unbiased sample

• Biased sample

At a middle school, the 7th graders will conduct a survey for where to go on a field trip.
Which method will result in the least biased decision?

• To randomly ask 8th grade students who went on a field trip last year.

• To randomly choose some 7th grade students to select a location.

4.  Carlos wants to know the favorite sport of people at his school so he asks his baseball team.

• Biased

• Unbiased

A company makes DVDs and randomly selects 25 from 1500 to test them to see if they work.

• Biased

• Unbiased

Tanya wants to know the percent of people likely to attend the upcoming musical at school. She asks each person in the musical how many people they know who are coming to make a prediction. Why is this sample biased?

• Drama students are more likely to lie.

• Musicals are better attended than plays.

• The drama teacher was not asked.

• The sample is not random and not representative of the entire school population.

Answer explanation

The sample is not random and not representative of the entire school population, as it only includes people involved in the musical, leading to bias.

Casey surveyed the members of his soccer team to ask them what their favorite sport is. Is this a biased sample or unbiased sample?

• Biased Sample

• Unbiased Sample

A real estate agent surveys people about their housing preferences at an open house for a luxury townhouse.

• Biased Sample

• Unbiased Sample

A school district wants to know if parents would prefer to get phone calls or emails from the schools. They survey the parents of all the seventh grade students enrolled in the district. Is this a biased sample or unbiased sample?

• Biased Sample

• Unbiased Sample

Shelley wants to survey grocery shoppers about their favorite brands. She goes to the store at 8am and surveys the first 50 people. Is this a biased sample or unbiased sample?

• Biased Sample

• Unbiased Sample

In a certain school, students can choose whether to eat in the school’s cafeteria. A reporter working for the school’s newspaper polled students on their reactions to changes in the menu at the cafeteria. For each student leaving the cafeteria in one 20-minute time period, the reporter used a die to determine whether to stop the student and ask how he or she felt about the new menu. In the reporter’s article it was stated that a random sample of the students showed that 23% of the school’s student population was happy with the new menu. Which of the following statements is true?

• Because each student leaving the cafeteria was randomly selected and could choose to answer or not, this is a random sample of the student population, and the 23% is an accurate measurement of the school population’s view of the new menu.

• Because students self-selected whether to eat in the cafeteria, the sampling method might be biased and the sample might not be representative of all students in the school.

• The survey would have been more effective if the reporter had collected the data in one 10-minute time period rather than in one 20-minute time period.

• The survey would have been more effective if students who cared about the food could have called the reporter to tell how they felt about the new menu, so that only students with opinions on the subject would have been surveyed.

• Because no treatment was imposed on the students eating in the cafeteria, one cannot make any conclusions about the new menu.