Biased Sampling

To determine the most popular children’s programs, a television station asks parents to call in and complete a phone survey.

• Biased Sample

• Unbiased Sample

To determine how often people eat out, every tenth person entering a Chinese restaurant is surveyed.

• Biased Sample

• Unbiased Sample

A senator wants to know how she is doing in her position. She sends a survey to 1000 registered voters in her party.

• Biased

• Unbiased

Karen surveyed the first seven shoppers at the produce stand.  Is this sample of shoppers at the produce stand likely to be biased?

• yes

• no

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.

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

• Biased Sample

• Unbiased Sample

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.

The sample should REPRESENT the population so you can INFER what the larger group is like.

If you take a BAD sample, it does not allow you to make inferences about the larger population.

Choose the option below that says "Biased Sample"

• A sample that accurately represents the population

• A sample that is selected randomly from the population

• Biased Sample

Susan polled 587 people throughout each city in her county.  Each city is the same size.  Is this sample of the residents of cities in the county likely to be biased?

• yes

• no

A teacher examined 17 different tests from each of her math classes.  Each class had the same number of tests.  Is this sample of the tests likely to be biased?

• yes

• no