Following the exclusion question, the next part of the questionnaire will be to screen the respondents for eligibility for the survey, depending on whether or not they belong to the research population. Few studies do not have a requirement for a screening section. In many surveys the researcher only wants to interview people with certain characteristics, demographic, behavioural or attitudinal. We do not wish to find out at the end of the interview that the respondent does not meet the criteria to be included in the sample definition.
Even where the sample is defined as being all adults, there will often be quota requirements on age or social grouping that have to be determined before proceeding with the interview.
It is common with face-to-face interviewing for demographic criteria not to be asked at the beginning but estimated by the interviewer, who confirms them only at the end of the interview. For gender this usually runs little risk, but for age and social grouping there is a clear risk that the estimation is incorrect. The interviewer discovers this error usually at the end of the interview when completing the classification details. The respondent may then fall into a different quota group than expected, or in a quota group that is already full, or outside any required quota grouping.
If the respondent falls outside any required quota group, the interviewer has to decide whether to discard the interview and possibly not be paid for it, or to send it in as part of the assignment and hope that it will be accepted because another interviewer has made a similar but compensating error. Unscrupulous interviewers may be tempted to falsify the data to make it appear that the respondent was in quota. Experienced interviewers make sure that they do not put themselves in this situation by checking with respondents at the beginning of the interview if there is any doubt and by estimating age and social grouping only at the beginning of the assignment, when all quota groups are still open. It can be difficult to ask questions such as these, which can be sensitive for some people, at the beginning of the interview, but ensuring that the respondent is in quota before the main interview begins can avoid wasted time and the temptation to falsify data later.
With all data collection methods other than face-to-face interviewing these questions must be asked at the beginning to ensure eligibility.
It is not uncommon for eligibility criteria to include both behavioural and attitudinal questions, or to include complex behavioural criteria. The screening questions can then take several minutes to administer and seem like an interview in their own right to respondents. Lengthy screening also takes up interviewer time, and if paper questionnaires are being used, may lead to errors in the assessment of eligibility. The complexity of the eligibility criteria should be a consideration in the survey design, and kept as simple and as straightforward to administer as possible.
As with the exclusion question, the interest of the researcher should be disguised in order to avoid ‘helpful’ respondents answering positively to everything, and to avoid the possibility of respondents trying to guess which answers they should give in order to be included or excluded as they wish. Respondents may also feel pressure to say that they have bought something when they have not, for fear of appearing mean or ungenerous, or lacking social status.
It is not good practice to ask, for example, ‘Have you bought a widescreen television in the last six months?’, as respondents’ reasons for answering ‘yes’ or ‘no’ may have little to do with whether they actually have or not. A less biased version of the question is given in Figure 3.1.
Source: Brace Ian (2018), Questionnaire Design: How to Plan, Structure and Write Survey Material for Effective Market Research, Kogan Page; 4th edition.