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Table 2 Reduced NHP38 version obtained through Classical Test Theory (CTT): the NHP20

From: Classical test theory versus Rasch analysis for quality of life questionnaire reduction

Original NHP38 items By dimension 1 st set of criteria for reduction: Discrimination (r) & Endorsement (p) 2 nd set of criteria for reduction: Factor analysis* NHP20
Dimension No. items α Items deleted as r < 0.40 Items deleted as P < 0.20 Items deleted as communality <0.30 Items deleted as main loading <0.40 Items deleted as difference between similar loadings ≤ 0.1 No. Items remaining
Energy (EN) 3 .76 - - - - EN2, EN3 1
Pain (P) 8 .90 - P2 - - P4, P5 5
Emotional Reactions (EM) 9 .82 EM8 - EM5, EM7 - - 6
Sleep (SL) 5 .81 SL1 - - - - 4
Social Isolation (SO) 5 .78 - SO2, SO3 SO4, SO5 SO1 - - 0
Physical Mobility (PM) 8 .83 - PM1, PM3 PM8 - - PM6 4
Summary Index 38 .95 (28 items remaining, α = 0.94)      20 (α = .92)
  1. * Principal Axis Extraction (4 factors) and Promax rotation (Factor intercorrelation range: 0.50 – 0.73) NHP items are: EN1-I'm tired all the time; EN2-Everything is an effort; EN3-I soon run out of energy; P1-I have pain at night; P2-I have unbearable pain; P3-I find it painful to change position; P4-I'm in pain when I walk; P5-I'm in pain when I'm standing; P6-I'm in constant pain; P7-I'm in pain when going up/down stairs; P8-I'm in pain when I'm sitting; EM1-Things are getting me down; EM2-I've forgotten to enjoy myself; EM3-I'm feeling on edge; EM4-These days seem to drag; EM5-I lose my temper easily these days; EM6-I feel as if I'm losing control; EM7-Worry is keeping me awake at night; EM8-I feel that life is not worth living; EM9-I wake up feeling depressed; SL1-I take tablets to help me sleep; SL2-I'm waking in the early hours ...; SL3-I lie awake for most of the night; SL4-It takes me long time to get to sleep; SL5-I sleep badly at night; SO1-I feel lonely; SO2-I'm finding it hard to contact people; SO3-I feel there is nobody I am close to; SO4-I feel I am a burden to people; SO5 I'm finding hard to get on with people;PM1-I can only walk about indoors; PM2-I find it hard to bend; PM3-I'm unable to walk at all; PM4-I have trouble getting up/down stairs; PM5-I find it hard to reach for things; PM6-I find it hard to dress myself; PM7-I find it hard to stand for long; PM8-I need help to walk about outside.