Table 2.

Items removed because of significant differential item functioning (UK compared with USA)

Domain item number	Item	UK (logit)	USA (logit)
Cough 6*	My cough disrupts my life	0.51	✓0.83
Mortality 27†	I often worry about how I might die	−0.16	✓0.56
Mortality 32†	I am afraid of being maintained at a poor quality of life	−1.01	✓0.13
Energy 37*	My level of physical energy makes me feel like I am lazy	0.44	✓0.69
Mental 39†	I feel weighed down by IPF	✓0.39	−0.12
Finances 58*	I am concerned that the cost of my care will use up my family's financial resources	−0.71	✓0.61
Finances 61†	Having IPF has forced me to reconsider my financial goals	✓0.50	0.02
Finances 62*	It has been difficult for me to make the necessary adjustments in my finances to provide support for my finances	✓0.85	0.75
Independence 4†	I occasionally ask for help to do things now that six months ago I could have done myself	−1.35	✓−0.38
Relations 76†	Living with IPF puts a strain on the relationship I have with member of my immediate family	✓0.39	0.17
Relations 80†	I am less willing to seek and form new relationships because I have IPF	−1.25	✓−0.81

✓=Less likely to respond ‘Strongly Agree’ to the item.

†Uniform differential item functioning.

*Non-uniform differential item functioning.