Psychometric characteristics of the Spanish version of instruments to measure neck pain disability.
BACKGROUND
The NDI, COM and NPQ are evaluation instruments for disability due to NP. There was no Spanish version of NDI or COM for which psychometric characteristics were known. The objectives of this study were to translate and culturally adapt the Spanish version of the Neck Disability Index Questionnaire (NDI), and the Core Outcome Measure (COM), to validate its use in Spanish speaking patients with non-specific neck pain (NP), and to compare their psychometric characteristics with those of the Spanish version of the Northwick Pain Questionnaire (NPQ).


METHODS
Translation/re-translation of the English versions of the NDI and the COM was done blindly and independently by a multidisciplinary team. The study was done in 9 primary care Centers and 12 specialty services from 9 regions in Spain, with 221 acute, subacute and chronic patients who visited their physician for NP: 54 in the pilot phase and 167 in the validation phase. Neck pain (VAS), referred pain (VAS), disability (NDI, COM and NPQ), catastrophizing (CSQ) and quality of life (SF-12) were measured on their first visit and 14 days later. Patients' self-assessment was used as the external criterion for pain and disability. In the pilot phase, patients' understanding of each item in the NDI and COM was assessed, and on day 1 test-retest reliability was estimated by giving a second NDI and COM in which the name of the questionnaires and the order of the items had been changed.


RESULTS
Comprehensibility of NDI and COM were good. Minutes needed to fill out the questionnaires [median, (P25, P75)]: NDI. 4 (2.2, 10.0), COM: 2.1 (1.0, 4.9). Reliability: [ICC, (95%CI)]: NDI: 0.88 (0.80, 0.93). COM: 0.85 (0.75,0.91). Sensitivity to change: Effect size for patients having worsened, not changed and improved between days 1 and 15, according to the external criterion for disability: NDI: -0.24, 0.15, 0.66; NPQ: -0.14, 0.06, 0.67; COM: 0.05, 0.19, 0.92.


RESULTS
Results of NDI, NPQ and COM were consistent with the external criterion for disability, whereas only those from NDI were consistent with the one for pain. Correlations with VAS, CSQ and SF-12 were similar for NDI and NPQ (absolute values between 0.36 and 0.50 on day 1, between 0.38 and 0.70 on day 15), and slightly lower for COM (between 0.36 and 0.48 on day 1, and between 0.33 and 0.61 on day 15). Correlation between NDI and NPQ: r = 0.84 on day 1, r = 0.91 on day 15. Correlation between COM and NPQ: r = 0.63 on day 1, r = 0.71 on day 15.


CONCLUSIONS
Although most psychometric characteristics of NDI, NPQ and COM are similar, those from the latter one are worse and its use may lead to patients' evolution seeming more positive than it actually is. NDI seems to be the best instrument for measuring NP-related disability, since its results are the most consistent with patient's assessment of their own clinical status and evolution. It takes two more minutes to answer the NDI than to answer the COM, but it can be reliably filled out by the patient without assistance.


BACKGROUND
Clinical Trials Register NCT00349544.
Kovacs
Francisco M
FM
Departamento Científico, Fundación Kovacs, Palma de Mallorca, Spain. kovacs@kovacs.org
Bagó
Joan
J
Royuela
Ana
A
Seco
Jesús
J
Giménez
Sergio
S
Muriel
Alfonso
A
Abraira
Víctor
V
Martín
José Luis
JL
Peña
José Luis
JL
Gestoso
Mario
M
Mufraggi
Nicole
N
Núñez
Montserrat
M
Corcoll
Josep
J
Gómez-Ochoa
Ignacio
I
Ramírez
Ma José
MJ
Calvo
Eva
E
Castillo
Ma Dolores
MD
Martí
David
D
Fuster
Salvador
S
Fernández
Carmen
C
Gimeno
Nuria
N
Carballo
Alejandro
A
Milán
Alvaro
A
Vázquez
Dolores
D
Cañellas
Montserrat
M
Blanco
Ricardo
R
Brieva
Pilar
P
Rueda
Ma Trinidad
MT
Alvarez
Luis
L
Del Real
María Teresa Gil
MT
Ayerbe
Joaquín
J
González
Luis
L
Ginel
Leovigildo
L
Ortega
Mariano
M
Bernal
Miryam
M
Bolado
Gonzalo
G
Vidal
Anna
A
Ausín
Ana
A
Ramón
Domingo
D
Mir
María Antonia
MA
Tomás
Miquel
M
Zamora
Javier
J
Cano
Alejandra
A
D000328:Adult; D000368:Aged; D003466:Cultural Characteristics; D004185:Disability Evaluation; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D019547:Neck Pain / Q000175:diagnosis*; D010147:Pain Measurement / Q000379:methods*; D011594:Psychometrics; D011788:Quality of Life; D015203:Reproducibility of Results; D013030:Spain; D011795:Surveys and Questionnaires; D014175:Translating