'Inaccurate' responses
The next two types of non-sampling error are caused by inaccurate information being obtained from the sampled individuals.
Instrument error
Instrument error usually results from poorly designed questions. Different wording of questions can lead to different answers being given by a respondent. The wording of the question may be such as to elicit some particular response (a leading question) or it may simply be carelessly worded so that it is misinterpreted by some respondents.
I am interviewing for the Smiths Confectionary Company. Do you prefer Smiths or Jones chocolate? |
The government intends to improve profitability of manufacturers by removing interest rate controls. Do you agree? |
How many workers do you employ in your farm? |
The first two questions are leading questions — it is clear which answer the interviewer is hoping for, and we are tempted to oblige! The third question will be clear to many respondents, but others employ seasonal or part-time workers and may answer this question in different ways.
Interviewer error
Interviewer error occurs when some characteristic of the interviewer, such as age or sex, affects the way in which respondents answer questions. For example, questions about racial discrimination might be differently answered depending on the racial group of the interviewer.
The diagram below is a small-scale illustration of a leading question. An interviewer asks 14 women...
I am interviewing for the Smiths Confectionary Company. Do you prefer Smiths or Jones chocolate?
Use the button Take sample a few times. Some respondents who really prefer Jones chocolate have stated that they prefer Smiths. As a result, the sample proportion preferring Smiths chocolate is higher than the proportion in the target population.