Spontaneous responses rarely tell the researcher the complete picture regarding what the respondent knows or feels, but only what is front-of- mind. However, most people find it difficult to articulate everything that they know or feel about a subject, or they forget that they know something, or they have given one answer and aren’t prepared to make further effort to think of additional answers. Prompting with a set of options tells the researcher what people know or recognize, rather than what is front- of-mind, if we are measuring awareness or recognition.
Alternatively, prompting helps people to recall actions and behaviour, and to express their answers in the framework desired by the researcher.
For prompted awareness questions that follow a spontaneous question on the same issue it may sometimes be helpful to include the phrase including any that you have already mentioned’. Whether or not this phrase is included, the analysis should always re-record any answers mentioned spontaneously on to the prompted recognition answer for each respondent.
With self-completion paper questionnaires it is not possible to ask both spontaneous and prompted questions on the same subject. Because respondents can read through the complete interview before answering questions, any lists or sets of answers that appear in the questionnaire can act as a prompt to any question.
Source: Brace Ian (2018), Questionnaire Design: How to Plan, Structure and Write Survey Material for Effective Market Research, Kogan Page; 4th edition.