Table 5.

Quotes illustrative of comprehension themes

Themes	Illustrative quotes
1. Understood the principle of an LHC and lung cancer screening	F_70_FS: ‘I like the way they do one, two, three, four….I like the headings and there's spaces in between and it's not too technically worded, I can understand everything that they're saying, it's quite explicit’. F_55_FS: ‘is this going to be a routine something in the way, when you're over as certain age, you get, you have your bowels tested regular after a certain age, is a lung screening thing going to become like that’. M_57_FS: ‘it tells you everything that's' going to be, what's going to be used and how it's done. And again, if you get in at an early stage you may get the cancer cells which is good as well’.
2. Understood the types of LHC results but assumed to clinically indicate the screening	F_58_FS: ‘Right, so you may or may not be offered a lung screening, cancer screening scan. So I don't know, I'm a wee bit confused, are the, why they only offer it to certain people… should it not just be beneficial to have it anyway?’ F_56_CS: ‘I think that should be put in, there's nothing available unless you've got a pronounced problem with your doctor, they're not going to just send you for a lung health check’. M‐61_CS: ‘Three options, no problems found, maybe a slight problem, they'll refer you to your GP, or if there's something there, they'll offer you a lung cancer screening scan, which I think can only be good’.
3. Misunderstood false negatives to be interval cancers	F_59_FS: ‘it still doesn't tell you why it could be missed because it said it can start growing after screening, well, that doesn't mean that they're missing it does it, that means it's not there when you have the scan’. F_55_CS: ‘Sounds like you can get cancer tomorrow, after screening, because you've had the radiation and it's made you get cancer’.
4. Poor understanding of radiation exposure due to an unfamiliar comparison	M_54_FS: ‘a CT scan's about the same as about one year's worth of radiation in the natural environment. I wouldn't have a clue what that would mean. But if it was compared to the amount, that maybe a CT scan is equivalent to ten X‐rays, I'd probably understand that better’. M_73_CS: ‘Well, what harm is in having a screening. As I say it's only like a low X‐ray, so you don't worry about having an Xray when you break your leg, do you, so. So I don't think, I can't see any harm in having it’.
5. Conflating understanding of the different types of abnormal lung cancer screening results	F_55_CS: ‘Isn't a further scan needed [the same as] an abnormal result? I don't know… they've seen something abnormal and you're going to need further tests. But on the further scan needed, it could be more serious, so what's the difference with what they're finding?’. M_58_FS: ‘incidental findings means there's something there but it's not going to be serious’. F_57_CS: ‘I like the bit that it can, picks up something even though they do not have lung cancer, obviously a false positive which means you've got something else wrong with your lungs and they can look at a further test’.
6. Outcome probabilities engaged deliberative thinking but overwhelmed those who found them too complex	F_59_FS: ‘I think it's easy to look at [icon array], you've got your thing there with all the colours’. F_55_FS: ‘So are they trying to tell me that lung cancer is not that high in the population or?… the way I'm reading it it's saying to me that three quarters of the population won't result in lung cancer but the other quarter will’. M_57_CS: ‘this really takes some looking at now and thinking about, lung cancer if they've not been screened…. Wow, this is a lot of information for my brain so now I feel some form of obsessive compulsive need to work out the percentages’.

Note: Participant codes (e.g., M_65_CS) represent participants' gender (M = male, F = female), age and smoking status (CS = current smoker, FS = former smoker).

Abbreviation: LHC, Lung Health Check.