Table 2

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

Domain item numberItemUK (logit)USA (logit)
Cough 6*My cough disrupts my life0.51✓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 lazy0.44✓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✓0.500.02
Finances 62*It has been difficult for me to make the necessary adjustments in my finances to provide support for my finances✓0.850.75
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✓0.390.17
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.