Unit 3 Sources of Bias

Bias

• A systematic error in measuring the estimate

  • Anything that causes the data to be wrong

• Favors a certain outcome

Sources of bias

Things that can cause bias in your sample (you can’t do anything with bad data)

Voluntary response

• People choose to respond

• Usually only people with very strong opinions respond

• The way to determine voluntary response is self-selection

Convenience sampling

• Ask people who are easy to ask

• Produces bias results

• Data obtained by convenience sampling will be biased

Under coverage bias

Some groups of the population are left out of the selection process

Nonresponse bias

Occurs when an individual chosen for the sample can’t be contacted or refuses to cooperate

Response bias

Occurs when the behavior of respondent or interviewer causes bias in the sample

• Results in an untruthful response

Wording of the questions

• Wording can influence the answers that are given:

  • Connotation of words

  • Use of “big” or technical words

  • Questions must be worded as neutral as possible to avoid influencing the response

  • The level of vocab should be appropriate for the population you are surveying