'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 Royal Society for the Prevention of Cruelty to Animals. Do you like dogs?
The government intends to improve profitability of farms by removing interest rate controls. Do you agree?
How many times have you been ill in the last year?

The first two questions are leading questions — it is clear which answer the interviewer is hoping for, and we are tempted to oblige! Some people will find the third question ambiguous — are ailments such as a slight cold or a slightly sprained ancle classified as 'illness'? (Asking whether the respondent had visited their doctor in the last year would avoid the ambiguity.)

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 Royal Society for the Prevention of Cruelty to Animals. Do you like dogs?


Use the button Take sample a few times. Some respondents who really do not like dogs have stated that they do. As a result, the sample proportion liking dogs is higher than the proportion in the target population.