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) | ||||