Sampling Methods - Unbiased and Biased Surveys

Sampling Methods - Unbiased and Biased Surveys

Vocabulary Start-Up

Statistics deal with collecting, organizing, and interpreting data. A survey is a method of collecting information. The group being studied is the population. Sometimes the population is very large. To save time and money, part of the group, called a sample, is surveyed.

What do you think?

A T.V. program manager wants to conduct a survey to determine which reality show is the favorite of viewers in a certain viewing area. He considers the following three samples below:

1. 100 people who are trying out for a reality TV show

2. 100 students at your middle school

3. Every 100th person at a shopping mall

Multiple Choice

Select the sampling method that would most fairly represent the people in the viewing area.

• 100 people that are trying out for a reality TV show

• 100 students at your middle school

• Every 100th person at a shopping mall

UNBIASED SAMPLES

To get valid results, a sample must be chosen very carefully. An unbiased sample is selected so that it accurately represents the entire population.

BIASED SAMPLES

In a biased sample, one or more parts of the population are favored over another. The results of a biased sampling method are invalid.

Let's Practice!

For the next several slides, determine whether each conclusion is valid by identifying the type of sampling method used for the survey.

Multiple Choice

To evaluate the defect rate of its memory chips, an integrated circuit manufacturer tests every 100th chip off the production line. Out of 10 chips tested, one chip is found to be defective. The manufacturer concludes that 3 chips out of 3,000 will be defective.

• Valid - Simple Random Sample

• Valid - Systematic Random Sample

• Invalid - Convenience Sample

• Invalid - Voluntary Response Sample

Multiple Choice

Students who wish to represent the school at a school board meeting are asked to stop by the office after lunch. After lunch, 5 students wish to represent the school.

• Valid - Simple Random Sample

• Valid - Systematic Random Sample

• Invalid - Convenience Sample

• Invalid - Voluntary Response Sample

Multiple Choice

To determine if the class understood the homework assignment, the math teacher checks the top 3 papers in the pile of collected homework. The teacher finds that all students understood the homework assignment.

• Valid - Simple Random Sample

• Valid - Systematic Random Sample

• Invalid - Convenience Sample

• Invalid - Voluntary Response Sample

Multiple Choice

A member of the cafeteria staff asks every fifth student leaving the cafeteria to rank 5 vegetables from most favorite to least favorite. She finds that corn is one of the favorite vegetables.

• Valid - Simple Random Sample

• Valid - Systematic Random Sample

• Invalid - Convenience Sample

• Invalid - Voluntary Response Sample

Multiple Choice

One bead for every member of the school orchestra is placed in a bag. All but 2 of the beads are white. Each member draws a bead from the bag, and the members who pick the non-white beads will represent the orchestra. It is predicted that two different instrument players will choose the white beads.

• Valid - Simple Random Sample

• Valid - Systematic Random Sample

• Invalid - Convenience Sample

• Invalid - Voluntary Response Sample

Multiple Choice

A real estate agent surveys people about their housing preferences at an open house for a luxury townhouse. He finds that most people prefer townhomes.

• Valid - Simple Random Sample

• Valid - Systematic Random Sample

• Invalid - Convenience Sample

• Invalid - Voluntary Response Sample

Multiple Choice

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

• Valid - Simple Random Sample

• Valid - Systematic Random Sample

• Invalid - Convenience Sample

• Invalid - Voluntary Response Sample

On your own...

Go complete the Quizizz practice: Biased and Unbiased Samples.