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Gathering Data and Types of Bias

Gathering Data and Types of Bias

Author: Al Greene
Description:

• Introduce the idea of bias and what it means for a sample that is supposed to be representative of a population
• Present the different types of bias, giving examples of how each can occur
• Review how randomization and correct sampling methods are the best defense against bias

This packet discusses types of bias that arise when you are collecting your data, and how to attempt to minimize those biases.

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Tutorial

Terms

Some terms that you are going to see in this packet include:

- bias

- undercoverage bias

- response bias

- nonresponse bias

- volunteer bias

- convenience sampling

Source: Greene

Types of Bias

This powerpoint defines the main types of biases that can arise when collecting a survey.

Source: Greene

Examples of Bias

For the following scenarios, decide which type(s) of bias is(are) present.

1. A surveyor is conducting a survey outside of a local library. He is asking people to take the survey as they come into the library.

a. Volunteer bias

b. Undercoverage

c. Response bias

d. Nonresponse bias

 

2. A magazine includes a questionnaire in one of its issues. The magazine is for guns and ammunition, and is asking about public opinion of gun control.

a. Volunteer bias

b. Undercoverage

c. Response bias

d. Nonresponse bias

 

3. A theatre company hands out a questionnaire about the quality of their productions. They are only interested in the people who attend the theatre. 

a. Volunteer bias

b. Undercoverage

c. Response bias

d. Nonresponse bias

Source: Greene

Examples solutions

 

1. A surveyor is conducting a survey outside of a local library. He is asking people to take the survey as they come into the library.

a. Volunteer bias

b. Undercoverage

c. Response bias

d. Nonresponse bias

Answer: a,b,d. The surveyor is asking people to be in the survey, so they have to volunteer for it. The surveyor is missing people who do not go to the library, so they are undercovered. They can also choose not to answer the questions after they realize what the survey is about, so that is a nonresponse bias.

 

2. A magazine includes a questionnaire in one of its issues. The magazine is for guns and ammunition, and is asking about public opinion of gun control.

a. Volunteer bias

b. Undercoverage

c. Response bias

d. Nonresponse bias

Answer: b,c,d. Anyone who doesn't subscribe to the magazine is being undercovered. The wording of the questions and the source of the survey may make people respond differently that they feel, so that is response bias. People can also choose not to send the survey back in, which is a nonresponse bias.

 

3. A theatre company hands out a questionnaire about the quality of their productions. They are only interested in the people who attend the theatre. 

a. Volunteer bias

b. Undercoverage

c. Response bias

d. Nonresponse bias

Answer: c,d. Since the people are in the theatre when they get the survey, they may be more generous with their review, fearing backlash from the theatre owners. People may also choose not to fill it out, once again making the nonresponse bias come into play.

Source: Greene