Updated norms of the MOS-SF36 in the young French population

The SF-36 is a generic quality of life questionnaire, massively translated and widely used to obtain physical and mental health status. However, validation work in the French language was carried out over a generation ago. The objective of this study was to obtain the norms of the SF-36 in the French young population. Method The 18 and years. Results The internal of the were high and the metrics associated with the factor structure were satisfactory. In general, women presented signicantly higher scores than men. Our results suggest that the SF-36 remains a reliable tool for studying quality of life in the young French population.


Introduction
Since the 1990s, health-related quality of life has gradually become a major theme in clinical research (Murdaugh, 1997). Indeed, although the health status of a population is most often expressed in quantitative terms such as life expectancy, mortality, or morbidity, a growing number of studies are now interested in measuring health status, and in particular its relationship with quality of life. These measures have placed the patient's perception at the centre of the assessment, by asking the patient about his or her subjective experience of his or her overall health status and more particularly about his or her functional status. Thus, a large number of self-reported questionnaires have been developed to measure these dimensions, notably the very broad Medical Outcomes Questionnaire 149-item from the RAND Health Insurance Experiment (Tarlov et al., 1989).
Several tools have been developed from this original questionnaire, including the derived SF-20 and SF-36 versions, which have shown more precise discriminatory abilities in their validation studies (McHorney et al., 1993). Thus, the Medical Outcomes Study Short Form (SF-36) has become one of the most widely used self-reported quality of life questionnaires for assessing health status, given its discriminatory properties of well-being at the level of clinical groups (Ware and Gandek, 1998), and has thus been used extensively in the monitoring of clinical practice outcomes and medical treatment effects. This questionnaire measures quality of life on the basis of eight dimensions or concepts that are frequently used in health studies. These eight dimensions are estimated from eight subscales that examine general health; mental health (with respect to anxiety and depression components); physical functioning; limitation of work capacity or daily activities due to physical functioning as well as that due to emotional disorders; vitality; pain; and social functioning.
The questionnaire has already been translated several times into French, and norms have been obtained for the French (Leplège, 2001) and Swiss (Richard et al., 2000) populations, but they were established almost a generation ago. The purpose of this study was to update the norms of the SF-36 in the young French population (18-39 years) and to reassess its psychometric properties in terms of reliability and validity.

Subjects
One thousand one hundred and thirty-four (n=1134) not preselected adults (mean age = 22.1 years ; SD = 3.2) from the general French population participated in this study. Participants screening was completed online, and ethical consents were obtained online in agreement with the Declaration of Helsinki. The study was approved by the "Comité de Protection des Personnes Sud-Est VI". Full measures were available for all subjects.

Questionnaire : the MOS-SF36
The SF-36 is a short 36-item behavioural questionnaire measuring eight quality of life dimensions: general health (GH -5 items), vitality (VT -4 items), bodily pain (BP -2 items), limitation of physical problems (RP -4 items), limitation of emotional problems (RE -3 items), mental health (MH -5 items), and physical functioning (PF -10 items), social functioning (SF -2 items). The SF-36 also includes an item to estimate the change in the subject's health status during the year preceding the assessment (HC).

Scoring
For each dimension, item responses were re-encoded on a scale ranging from 0 (best) to 100 (worst), following the standard SF-36 scoring algorithm (Ware Jr, 1999), adapted for a 5-point Likert scale. The algorithm used is available in Table 1.

Factor structure
In order to test our 8-factors model for SF-36 and assess construct validity, we conducted a con rmatory factor analysis. Generalized least squares method was performed in order to test the t capability of the factor structure. Model t was assessed using the following t indices : we used the χ2 test statistic for absolute t ; the comparative t index (CFI) and Tucker-Lewis Index (TLI) for t relative to a null model (Bentler, 1990

Descriptive statistics
Descriptive statistics of the study sample are shown in Table 2. Results showed that women reported poorer health compared to men for all variables except for BP.

Internal consistency and reliability
Results concerning internal consistency and reliability are presented in Table 3. Data showed that the SF-36 questionnaire carries high internal consistency and reliability even when an item is dropped. Con rmatory factor analysis Con rmatory factor analysis suggested that the 8-factor model t well with the SF-36 questionnaire, except for the CFI and TLI which remains slightly below the pre-de ned cut-off [χ2=2508, p<.001, CFI=.893, TLI=.88, RMSEA=.057, SRMR=.052]. We assumed that, based on these indices, this sample has an acceptable t to the 8-factor model.
Justi cation of the normative approach

Normative values
Normative data for the SF-36 composite scores expressed in percentiles are presented in Table 4. The full percentiles for the 8 subscales, the 2 composite factors and HC item are available in Supplementary  Tables 1-11. Women showed higher scores compared to men for each scale except for BP.

Discussion
The present study veri ed the reliability and the construct validity of the French version of the 36-Item Short Form Survey (SF-36) questionnaire in a young population.
We then performed a factor analysis that suggested some gender differences in self-reported responses, with women reporting lower quality of life than men for all domains studied except BP, which is coherent with previous studies in France and over the world (Demiral et

Conclusion
We concluded that the French SF-36 is a reliable questionnaire for the assessment of physical and mental health conditions. The study provided norms of SF-36 for the young French population and for both genders.
Declarations AUTHOR'S CONTRIBUTIONS AT created the experimental protocol. ET collected the data. AT and ET performed the statistical processing of the data, the production of the tables, and wrote the paper. JD, BB, and MM supervised the work.

Not applicable
Ethics approval and consent to participate The study was approved by the Comité de Protection des Personnes Sud-Est VI (protocol number : 20.02.24.42827). Consent was obtained online before the completion of the survey. The research was performed in accordance with the Declaration of Helsinki.

Consent for publication
Not applicable.

Competing interests
Not applicable.

Data availability
The datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request.