Table 2 Examples of cognitive interview probes

• Which answer would you choose? Why?

• Was it easy or difficult to answer this question?

• I noticed you were spending some time with that question – can you tell me what you were thinking about?

• You chose X. Why? How does X differ from Y or Z?

• I noticed you were looking here, what were you thinking?

• What does ‘[phrase or word from questionnaire]’ mean to you? Would you be able to explain that in your own words?

• You answered differently for how you think the person you know would answer, why is that?

• Could this question be made clearer? If so, in what way?