Errors of Commission

Errors of commission are sometimes also called "false positives." They refer to instances in which someone or something is erroneously included for consideration when they or it should have been excluded. In survey research, this error typically occurs when the eligibility of a unit is determined. For example, when someone is screened at the start of interviewer contact to determine whether or not he or she is eligible, and the person answers erroneously in a way that makes the interview proceed as though the person were eligible for data collection when in fact the person is not eligible, then this is an error of commission. In these cases, data are gathered and analyzed for someone who should not have been interviewed.

Errors of commission occur for many reasons, but most are due to questionnaire-related error, interviewer-related error, and/or respondent-related error. The introduction to a questionnaire, where eligibility screening is typically carried out, might be worded poorly and thus cause incorrect data to be gathered, leading to people who in fact are not eligible being erroneously treated as eligible. An interviewer may administer an eligibility screening sequence poorly, thus causing the respondent to misunderstand what is being asked, leading to answers that result in an ineligible person being treated as eligible. Finally, a respondent may be unable to understand the eligibility screening questions and thus may give incorrect answers. Or the respondent may not be paying enough attention to the screening questions or may not be willing or able to give an accurate answer. In fact, some respondents will give an answer they believe will disqualify them even if it is not true for them, whereas others will do the opposite just so they can take part in the survey.

An example of errors of commission routinely occurs when people in the United States are sampled via telephone by the Nielsen Company to ask them to participate in a week-long TV diary survey. In the age of time shifting, when many people have digital video recorders (DVRs) that allow them to shift the time they view television programming, a special diary has been devised to measure programming that is time-shifted. This diary places much more of a cognitive burden on respondents who receive it than does the regular TV diary that does not measure time shifting. Thus, it would be ideal if only those people who have DVRs were sent the special diary. However, despite extensive R&D testing of the eligibility questions that are used to determine whether or not someone has a DVR, many people (especially older adults) appear not to be able to accurately answer the questions and therefore incorrectly are sent the special diary when they should receive the simpler diary.

Another example of errors of commission concerns the current situation in the United States when interviewing people reached via cell phone. Currently there are federal regulations affecting number portability that allow people to take their cell phones to another state without changing their numbers when they move. If, for example, a telephone survey of residents of New York were to be conducted without adequate screening to determine whether or not the person reached was in fact a New York resident, then all those people who had cell phones with New York area codes but now were living in other states would incorrectly be treated as eligible.

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