woman holding clipboard with survey

Randomization is one important way to make sure that survey data can be used to reach valid conclusions.

Another factor that may influence the conclusions reached by survey data is bias. A survey has bias if the survey data has a tendency to overestimate or underestimate a particular characteristic that is being surveyed. In other words, the results of the survey are tilted toward one particular viewpoint.

Bias can result from a variety of sources. One type of bias, selection bias, results from the selection of a sample that is not representative of the population being described.

Another type of bias, response bias, can come from the way that a survey instrument itself is constructed.

Interactive exercise. Assistance may be required.

Sort the examples of bias below into two types of bias: selection bias and response bias.

Practice

For the following questions, determine if the sample is representative of the population or not.

  1. A neighborhood organization wants to know how many people in the neighborhood would support a new bus route, so they survey every fourth person exiting a bus on an existing route.

    2. Interactive popup. Assistance may be required.

    Check Your Answer

    The sample is not representative. The population is the people that live in the neighborhood, but the sample is only people who are riding an existing bus. Close Pop Up

  2. Margie wants to know how many people are likely to take a new Computer Technology course in her school, so she surveys every fifth person entering school on Tuesday.

    3. Interactive popup. Assistance may be required.

    Check Your Answer

    The sample is representative. The population is all students in Margie’s school, and the sample is a randomly selected portion of all students in the school. Close Pop Up

  3. Ruben wants to know which city is a favorite vacation spot for people in his city, so he surveys every third person in line to board an airplane to Las Vegas at the city airport.

    4. Interactive popup. Assistance may be required.

    Check Your Answer

    The sample is not representative. The population is the people that live in Ruben’s city, but the sample is only people who are boarding an airplane to Las Vegas. Close Pop Up

  4. Aleshia wants to know how students at Robertson Middle School feel about the temperature of their classrooms, so she surveys all students in her English class.

    5. Interactive popup. Assistance may be required.

    Check Your Answer

    The sample is not representative. The population is all students at Robertson Middle School, but the sample is only students in Aleshia’s English class. Close Pop Up

  5. Spiral Review Question: Using a randomly selected survey that is representative of 8th grade students at Rodriguez Middle School, Brandon has determined that 65% of students plan to vote for Selena as the 8th Grade Prom Queen. If there are 440 students in the 8th grade at Rodriguez Middle School, and all of them vote, how many will NOT vote for Selena?

    6. Interactive popup. Assistance may be required.

    Check Your Answer

    35% of 440 students, or 154 students Close Pop Up