## 2 Materials and Methods
### Analysis of Data  
For the descriptive analysis carried out through frequencies (%), means (M) and standard deviations (SD), the statistical software SPSS 25.0 (IBM Corp, Armonk, NY, USA) was used, as well as the Cronbach's alpha to determine the internal consistency of the instruments, establishing the reliability index at 95%. A multigroup analysis of the structural equations was developed with AMOS software version 23.0 (IBM Corp., Armonk, NY, USA). The level of significance was established at 0.05 using [PERSON]'s chi-square test.  
The structural equation model (SEM) was used to establish the relationships between variables that make up the theoretical model (Figure 1) for both groups (male and female gender). A general model was carried out to establish the relationships of the study population and two differentiated models in order to verify the existing associations between the variables and as a function of gender. The SEM developed was elaborated from five observable variables that provided explanations of the relationships. The causal explanations of the variables were made considering the reliability of the measurements and the associations observed between the indicators. Measurement errors for endogenous variables were included in order to control them directly and interpret them as multivariate regression coefficients. The two-way arrows (covariances) connect the exogenous variables, while the one-way arrows reveal the direct and indirect effects between the endogenous variables. The estimation of the parameters was made using the maximum likelihood estimation method, since it is coherent, unbiased and not affected by the type of scale. Similarly, the level of significance established through [PERSON]'s chi-square test was 0.05.  
For the present SEM, self-concept (SC), Mediterranean diet (MD) and problematic use of videogames (PUVG) acted as endogenous variables (represented by a square). Sleep duration (hours per day) (SD) and physical activity (minutes per day) (PA) act as exogenous variables (represented by an ellipse). The exogenous variables SD and PA exert an effect on the endogenous variables SC, MD and PUVG. In addition, the MD and PUVG are affected by SC. Finally, there is a bidirectional effect between SD and PA.  
The fit of the model was examined to verify the compatibility, and the empirical data were obtained. Reliability of fit was assessed using [PERSON]'s goodness indices [29]. These parameters indicate that the non-significant values in the chi-square associated with p indicate a good fit of the model. Because this statistic is highly sensitive to sample effects, other fit indices should be used [30]. In this sense, and taking into account various parameters, the comparative fit index (CFI) will be acceptable with values greater than 0.90 and excellent with values greater than 0.95. For the normed fit index (NFI), values must be higher than 0.90. The Tucker-Lewis index (TLI) will be acceptable if it presents values higher than 0.90 and excellent with values higher than 0.95. Finally, the root mean square error of approximation (RMSEA) will be acceptable if it is less than 0.08 and excellent with values less than 0.05.  
Figure 1: Theoretical structural equation model. Note: Sleep Duration (hours per day) (SD); Self-Concept (SC); Physical Activity (minutes per day) (PA); Mediterranean Diet (MD); Problematic Use of Videogames (PUVG).