Development of the Italian version of the Neck Pain and Disability Scale, NPDS-I: cross-cultural adaptation, reliability, and validity.
METHODS
Evaluation of the psychometric properties of the Neck Pain and Disability Scale (NPDS).


OBJECTIVE
Translating, culturally adapting, and validating the Italian version of the NPDS-I.


BACKGROUND
Great importance is devoted to validated and comprehensive outcome measures to improve interventions for neck pain. A translated form of a functional scale in patients with neck pain has never been studied within the Italian population.


METHODS
The Italian version of the NPDS questionnaire was developed involving forward-backward translation and final review by an expert committee to establish multidimensional correspondence with the original English form. Psychometric testing included factor analysis with Varimax rotation, reliability by internal consistency (Cronbach's alpha) and test-retest repeatability (Spearman's rank test), validity by comparing the Italian version of SF-36 to NPDS-I (Pearson's correlation); further subscales comparisons to single SF-36 domains were also conducted.


RESULTS
The authors required a 4-month period before achieving a shared version of the NPDS-I. The form was administered to 157 subjects, presenting good acceptability. Factor analyses demonstrated 3 subscales (63% of explained variance), defined as neck dysfunction related to general activities (subscale 1, 8 items), neck pain and cognitive-behavioral aspects (subscale 2, 8 items), neck dysfunction related to activities of the cervical spine (subscale 3, 4 items). The questionnaire showed high internal consistency (NPDS: 0.942, subscale 1: 0.919, subscale 2: 0.856, subscale 3: 0.889) and good test-retest reliability (P < 0.001). Validity was explained by high correlations with SF-36 total score (r = -0.47, P < 0.001) and with single SF-36 domains scores, highly significant (P < 0.001) with the exception of physical role domain (r = -0.17, P = 0.035). Finally, the 3 subscales demonstrated good correlations when compared with selected SF-36 domains.


CONCLUSIONS
The NPDS-I outcome questionnaire was successfully translated into Italian, showing good multidimensional and psychometric properties, supporting the results of the already existing versions of the scale. Its use is recommended in clinical and research practice.
Physical Medicine and Rehabilitation Unit, Scientific Institute of Lissone (Milan), Recovery and Care Scientific Institute, IRCCS Salvatore Maugeri Foundation, Milan, Italy. marco.monticone@fsm.it
Marco
M
Monticone
Paola
P
Baiardi
Nicola
N
Nido
Claudia
C
Righini
Alessandro
A
Tomba
Elena
E
Giovanazzi
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D003431:Cross-Cultural Comparison; D004185:Disability Evaluation; D005163:Factor Analysis, Statistical; D005260:Female; D006801:Humans; D007558:Italy; D007802:Language; D008297:Male; D008875:Middle Aged; D019547:Neck Pain / Q000175:diagnosis*; D010147:Pain Measurement / Q000592:standards; D011237:Predictive Value of Tests; D011594:Psychometrics; D015203:Reproducibility of Results; D011795:Surveys and Questionnaires / Q000592:standards