Box 1.

Search strategy.

1. patient reported outcomes.ti,ab.(6383) 2. quality of life.ti.ab.(266914) 3. health status.ti,ab.(175146) 4. global health.ti.ab.(53851) 5. health related quality of life.ti.ab.(53363) 6. outcome measurement.ti.ab.(26871) 7. 1 or 2 or 3 or 4 or 5 or 6(491494) 8. classical test theory.ti.ab.(1460) 9. validity.ti.ab(205095) 10. reliability.ti.ab.(162542) 11. content validity.ti.ab.(16710) 12. confirmatory factor analysis.ti.ab.(17892) 13. exploratory factor analysis.ti.ab.(13537) 14. internal consistency.ti.ab.(39236) 15. test-retest.ti.ab.(30481) 16. psychometr*.ti.ab.(66358) 17. known group.ti.ab.(108113)

18. Rasch.ti.ab.(5442) 19. DIF.ti.ab.(2784) 20. 8 or 9 or 10 or 11 or 12 or 13 or 14 or 15 or 16 or 17 or 18 or 19 or 20 or 21 (998874) 21. child*.ti.ab.(1286933) 22. neonat*.ti.ab.(185516) 23. adolescent*.ti.ab.(308550) 24. pediatric*.ti.ab.(213646) 25. paediatric*.ti.ab.(48497) 26. 23 or 24 or 25 or 26 or 27 (1715918) 27. 7 and 22 and 28 (7138) 28. 29 limited to Human and English Language and Age Groups All Child Age 0–18 years (4849) 29. Duplicates removed 1398 30. Total 3451