Table 3 Case examples for the major problems

Comprehension of the wording and underlying concepts

- R (female 81, DE), NHIS-PAQ: “As I am a retired person, I have actually always leisure time, I can do everything how I want it to, except my household works or appointments, as today…”.

- R (male 45, DE), NHIS-PAQ: There is no definition of ‘leisure time’ for him because of his job, which is not a usual one; he is not a typical employee (self-employed). Problematic, because for him there is not a difference between work and leisure time.

- R (male 74, DE), NHIS-PAQ: “As a retired person you arrange your duties that they are distributed along the whole day, so I virtually do not have any leisure time [laughed].”

- R (male 70, DE), NHIS-PAQ: “You have to distinguish between an employed and a retired person. For me (retired) everything is leisure time. When I used to work, it was the time after work”.

- R (female 41, DE), IPAQ-SF: R had problems to understand the question, asked for response categories. She said the question was okay to answer, but while answering the questionnaire she really had problems to understand it.

Recalling instances and activities

- R (male 31, UK): R says that IPAQ-SF is harder to answer than NHIS-PAQ: It is a lot more to remember, it is wordy and difficult to follow what is being included and excluded, and it is difficult to make a quick calculation to work out the activity duration.

- R (male 74, DE): NHIS-PAQ was easy to answer for him because he does not do these kind of activities.

- R (male 21, DE), NHIS-PAQ, interviewer observation: R has to think for a long time and wonders whether he should include work (until I tell him, that this part of the questionnaire is just about leisure time).

- R (male 17, DE), IPAQ-SF: R seems a little worried about the difference between ‘last seven days’ and ‘usually’; he was on holidays for skiing and is therefore quite confused about what to answer.

- R (female 59, DE), IPAQ-SF: She only thought about work-related activities, so the duration of vigorous PA might be too short; IPAQ-SF moderate activities: Her answer deals with cycling in leisure time, during the interview she said, she is going to work by bike every day; so here her answer might be an underestimation.

Classifying activities into the answer options

- R (female 26, UK): R felt that she contradicted herself when talking about ‘vigorous’ in NHIS-PAQ to which she gave different answers in IPAQ-SF. The way the descriptions were presented, made her think of the same term in 2 different ways. She does not get into a heavy sweat [NHIS-PAQ] but does do activities that need ‘hard physical effort’ as described in IPAQ-SF. R did not understand ‘moderate,’ as in both Sets, they also had different definitions. For ‘moderate activities’ she answered ‘yes’ in NHIS-PAQ and ‘no’ in IPAQ-SF.

- R (female 26, UK), IPAQ-SF: “If you’re trying to identify the types of exercise I do, there surely is a simpler way of finding-out what and how regularly I exercise (…). It seemed like I had to slot them into the descriptions, which wasn’t easy to do. I wasn’t sure I was answering them correctly, even thought I was sure of the activity I was doing, I didn’t know if I was answering them appropriately or accurately”.

- R (female 33, EE), IPAQ-SF: R is confused about what to consider and what not: “In some questions it is necessary to take walking into account and in others not. Is sportive walking included to walking or not? All depends on the intensity, after all”.

- R (female 42, BE), IPAQ-SF: “The distinctions that have to be made are difficult because everything is linked in one activity”.

- R (female 62, UK), IPAQ-SF: R included a vigorous walk in Q1. This made it difficult for her to answer Q3; without the walks she had to say that she did no moderate activity. When she came to Q5 she thought she answered wrong and was confused; her vigorous walk potentially could fit in either section.

- R (female 73, DE), NHIS-PAQ: R talks about her gymnastics, thought about sweating, then answers Q8. R describes again her gymnastics and answers Q10. R describes again her gymnastics that are also strengthening, she seems annoyed that questions are very similar, and answers Q12.

- R (female 26, UK): She was including all of her physical activities when she was answering NHIS-PAQ; she was not restricting herself to leisure activities. She was also including work.

Calculating frequencies and durations

- R (male 43, UK), NHIS-PAQ, interviewer observation: The problem that I had was the R didn’t answer the questions in the way they were intended. The first difficulty was fitting in what the R was telling me to the answer options available. The more he explains the more difficult it is to answer the questions. He goes to the gym 3 times a week for an hour at a time and goes jogging every day between 30 and 45 min. He is not sure to say 1h 45mins a day or 45min a day (to use a day at the gym or a day when he doesn’t go to the gym.). The second difficulty was the R answering that he did light to moderate exercises all day everyday, he failed to give me time periods.

- R (female 42, BE), IPAQ-SF: “I can’t remember what I answered and I can’t even tell how I calculated”.

- R (female 60, BE), IPAQ-SF: “Everything is relative what we can call vigorous. For me vacuuming is vigorous, I’ve done it 4 times this week, for others it is of course moderate”.

- R (female 81, DE), IPAQ-SF: “I just approximated the time for sitting and walking, it is so difficult to estimate because it is s.th. so normal”.