Differential item functioning (DIF) of SF-12 and Q-LES-Q-SF items among french substance users.
BACKGROUND
Differential Item Functioning (DIF) is investigated to ensure that each item displays a consistent pattern of responses irrespective of the characteristics of the respondents. Assessing DIF helps to understand the nature of instruments, to assess the quality of a measure and to interpret results. This study aimed to examine whether the items of the Quality of Life Enjoyment and Satisfaction Questionnaire-Short Form (Q-LES-Q-SF) and Short-Form 12 (SF-12) exhibit DIF.


METHODS
A total of 124 outpatients diagnosed with substance dependence participated in a cross-sectional, multicenter study. In addition to the Q-LES-Q-SF and SF-12 results, demographic data such as age, sex, type of substance dependence and education level were collected. Rasch analysis was conducted (using RUMM2020 software) to assess DIF of the Q-LES-Q-SF and SF-12 items.


RESULTS
For SF-12, significant age-related uniform DIF was found in two of the 12 items, and sex-related DIF was found in one of the 12 items. All of the observed DIF effects in SF-12 were found among the mental health items. Three items showed DIF on the Q-LES-Q-SF; however, the impact of DIF item on the delta score calculation for the comparisons of self-reported health status between the groups was minimal in the SF-12 and small in the Q-LES-Q-SF.


CONCLUSIONS
These results indicated that no major measurement bias affects the validity of the self-reported health status assessed using the Q-LES-Q-SF or SF-12. Thus, these questionnaires are largely robust measures of self-reported health status among substance users.
Service Médico Psychologique Régional, 57 073, Metz, France. steph_bedes@yahoo.fr.|CSAPA (Health Care Centre of Accompaniment and Prevention in Addictology), University Hospital of Nancy, Nancy, France. steph_bedes@yahoo.fr.|EA4360 APEMAC, University of Lorraine, Nancy, France. steph_bedes@yahoo.fr.
Stéphanie
S
Bourion-Bédès
CSAPA (Health Care Centre of Accompaniment and Prevention in Addictology), University Hospital of Nancy, Nancy, France. raymund.schwan@univ-lorraine.fr.
Raymund
R
Schwan
CSAPA (Health Care Centre of Accompaniment and Prevention in Addictology), University Hospital of Nancy, Nancy, France.
Vincent
V
Laprevote
ANPAA 15- CSAPA (Health Care Centre of Accompaniment and Prevention in Addictology), Saint-Flour, Cantal, France. bedesams@club-internet.fr.
Alex
A
Bédès
ANPAA 15- CSAPA (Health Care Centre of Accompaniment and Prevention in Addictology), Aurillac, Cantal, France.
Jean-Louis
JL
Bonnet
EA4360 APEMAC, University of Lorraine, Nancy, France. c.baumann@chu-nancy.fr.|ESPRI-BioBase Unit, PARC, University Hospital of Nancy, Nancy, France. c.baumann@chu-nancy.fr.
Cédric
C
Baumann
D000328:Adult; D003430:Cross-Sectional Studies; D005163:Factor Analysis, Statistical; D005260:Female; D005602:France; D006801:Humans; D008297:Male; D008603:Mental Health; D008875:Middle Aged; D011594:Psychometrics; D011788:Quality of Life / Q000523:psychology*; D015203:Reproducibility of Results; D019966:Substance-Related Disorders / Q000523:psychology*; D011795:Surveys and Questionnaires / Q000592:standards*; D055815:Young Adult