Validity of the Severity of Dependence Scale (SDS) construct applying the item response theory to a non-clinical sample of heroin users.
OBJECTIVE
The purpose of this work is to study the validity of the Severity of Dependence Scale (SDS) construct by applying Rasch models to a non-clinical sample of heroin abusers.


METHODS
982 (73% men) young people 30 years old or under (mean age 25.9 years) participated. All of them were captured from the community in the metropolitan areas of Madrid, Barcelona and Seville, between April 2002 and December 2003.


METHODS
Dimensionality of the scale and calibration of items were studied using the Rating Scale model, which is a Rasch-type model. A factorial analysis was also performed to check the dimensionality of the scale.


RESULTS
The analysis of fit shows that all the items have infit and outfit values between +/- 2 logits, indicating that the data fit the model and that it may be assumed to be unidimensional. The principal components analysis also showed the existence of a principal factor that explains 52.5% of the variance observed. Item calibration found that they are between +0.89 and -1.04 logits on the scale.


CONCLUSIONS
The results show unidimensional structure of the SDS scale. Item calibration shows they are distributed along the continuum, which must be taken into account when calculating total scores. The study's limitations are noted.
Gonzalez-Saiz
Francisco
F
Fundacion Andaluza para la Atencion a las Drogodependencias, Sevilla, Spain. pacogonzalez@comcadiz.com
Lozano
Oscar M
OM
Ballesta
Rosario
R
Silva
Teresa
T
Brugal
Maria Teresa
MT
Bilbao
Izaskun
I
Barrio
Gregorio
G
Domingo-Salvany
Antonia
A
Bravo
Maria Jose
MJ
De la Fuente
Luis
L
Del Proyecto Itinere
Grupo
G
D000328:Adult; D003625:Data Collection / Q000706:statistics & numerical data; D005163:Factor Analysis, Statistical; D005260:Female; D006556:Heroin Dependence / Q000175:diagnosis* / Q000453:epidemiology / Q000523:psychology; D006801:Humans; D008297:Male; D015233:Models, Statistical; D025341:Principal Component Analysis; D011336:Probability; D011569:Psychiatric Status Rating Scales / Q000706:statistics & numerical data*; D011594:Psychometrics; D015203:Reproducibility of Results; D012720:Severity of Illness Index; D013030:Spain / Q000453:epidemiology