Table 4.

Content Validity of the WF-NRS

Exemplary participant quotes from cognitive debriefing interviews
Topic	Quote
Understandability	If I’d had any worse in the last 24 hours, which last night was one of those nights that wasn’t a good night and I think I was up four or five times, you know?
	“ … there’s just that little period once I’ve been home for a half hour, 45 minutes and then after I’ve been home for, you know, over an hour, it’s just – that’s when I’m the most tired and then I kind of get my second wind… So I’d say it’s just that period after work where I move up to about a six.”
	“So if you want to ask me what my worst level of fatigue is, maybe – again, I don’t – these were just all kind of – I always think if they’re trying to get a trick question out of me, so “Best describes your worst level of fatigue during the past” – I don’t know. That worst kind of throws me off by that. Because isn’t fatigue bad anyways, no matter how you look at it?
Response scale	“How did I decide? Wait a minute. No fatigue. Oh, I meant to do it the other way. I really meant the other way. So that really should have been at this end…Oh, ok. I’m sorry I misread that one. I would think around a 7. It’s, you know, it’s as bad as you can imagine. I would think maybe an 8. Can I change it?
Recall period	“… Depending on what the person is doing every 24 hours – at least for me every 24 hours is different… so I understand that you’ve got to put a time on the stuff, but the last 24 hours for me is different than the middle of the week 24 hours of the last week.”
	“Yeah, I think that’s, kind of – I probably should do one of these every day, that way I would know exactly how I feel every day, you know, because it just makes you realize just how tired you are or how it affects your daily life, you know, so, very interesting.”
	“For me, I – 24 hours, it depends on what – for me, I would look at a week, because I think during the course of a week you will see – there’s a – and I don’t know how everybody else is, but I just know during the course of a week there could be a week that’s good, there could be a week that has a day or so that’s not so good, you know, and that’s just…: I just think you’ll get a bigger picture by looking at it over a course of a week.”
Possible mediating factors and adjustments	“I haven’t felt like I’ve rested well.”
	“That was just I pretty much wore myself out, just of the things that I did and the fact that I think my body doesn’t work as fast, you know, there’s always the pain and the stiffness, so therefore, to me, you know, it’s – that causes the fatigue to really, you know, get worse, so…I just thought to myself that that’s just how I felt, that I just really, you know – I really don’t know how to explain it. It’s not that I just want to you know, lie down and sleep all the time. It’s just that you just feel like you never – with the stiffness and the pain it just never gives you a feeling of you’ve really had a good rest. You’ve really had a good, you know, it’s just really hard to, and that’s why I put eight because that’s what I felt, you know, I haven’t felt like I’ve rested well, you know, so, I don’t know.”
	“Now 10 is almost like crawling into bed and, you know, and listening to something and having a difficult time just filtering and, you know, and just – that’s severe. And what’s amazing is that – I don’t want you to think that there is, you know, it’s – it’s not a mental problem. It’s like you’re so fatigued that it’s just difficult to process the info, you know, I dunno.”
	“When my mother came into my room I actually snapped at her, you know? I didn't mean to and I felt really bad.”
	“… because you do kind of adjust 'cause in your mind you do think, what – and that’s why, I guess, I go back to that day that I say that was my worst day because in my mind I can kind of know what I’ve done …”