In collecting primary data, marketing researchers have a choice of two main research instruments—the questionnaire and mechanical devices. The questionnaire is by far the most common instrument, whether administered in person, by phone, or online. Questionnaires are very flexible—there are many ways to ask questions. However, they must be developed carefully and tested before they can be used on a large scale. A carelessly prepared questionnaire usually contains several errors.

In preparing a questionnaire, the marketing researcher must first decide what questions to ask. Questionnaires frequently leave out questions that should be answered and include questions that cannot be answered, will not be answered, or need not be answered. Each question should be checked to see that it contributes to the research objectives.

The form of each question can influence the response. Marketing researchers distinguish between closed-end questions and open-end questions.

• Closed-end questions include all the possible answers, and subjects make choices among them. Examples include multiple-choice questions and scale questions. Closed-end questions provide answers that are easier to interpret and tabulate.

• Open-end questions allow respondents to answer in their own words. In a survey of airline users, Delta might simply ask, “What is your opinion of Delta Airlines?” Or it might ask people to complete a sentence: “When I choose an airline, the most important consideration is. . . .” These and other kinds of open-end questions often reveal more than closed-end questions because respondents are not limited in their answers. Open-end questions are especially useful in exploratory research, when the researcher is trying to find out what people think but not measuring how many people think in a certain way.

Researchers should also use carefully in the wording and ordering of questions. They should use simple, direct, unbiased wording. Questions should be arranged in a logical order. The first question should create interest if possible, and difficult or personal questions should be asked last so that respondents do not become defensive.