In all the studies on evaluation of the SRH, a single question was used “How would you rate your health in general?”[6
] However, in this study, we have combine 12 items (including this question, as well) by using the latent class models and have obtained a single dichotomous item. This method is more general because includes physical and emotional sense of adolescents health.
Among all independent variables entered the model, only physical activity, smoking, family smoking, hygienic habits, family history of disease and violence were statistically associated to SRH.
In cross-sectional studies, associations between physical activity and SRH in children and adolescents have been evaluated, which show that powerful activity is associated with good SRH. In this study, physical activity had a positive effect on good SRH. It means that students who more active, more likely report their health good. Similar findings have been reported in a Swedish cohort study on 15 years old students and in a cross-sectional study on 11-12-year old boys and girls from the United Kingdom, which showed that SRH was significantly related to whether or not the adolescents were currently exercising in both genders.[25
Countless studies have shown statistically significant relationship between smoking status and poor SRH. In these studies, a higher level of health was reported among adolescent who were at a lower level of tobacco use.[10
] In our study, t-test analysis and parametric analysis showed that the smoking was not associated with SRH linearly, but it had a non-linear impact on SRH. We can see this non-linearity in the plot . In general, its diagram has a descending pattern.
Exposure to violence associated to SRH as smooth effect only. The smooth effect has been shown in . This variable in childhood and adolescence constitutes a pervasive public health problem.[30
] The study on the US adolescent indicated that as individuals were exposed to increasing amounts of violence, their SRH would decline.[27
] Another article examined the effects of harassment and victimization on self-rated and mental health status among Canadian adolescents aged 16-17. This study concluded that harassment at school was found to be a robust predictor of children's self-reported and mental health status.[26
] However, our study was in agreement with this study in showing the descending effect of violence on SRH.
The family smoking had linear and non-linear relationships with to SRH. The sign of its coefficient is negative. So it is negatively associated to a high SRH. This result confirmed the study which was about the role of parents on adolescents’ SRH.[28
We could not find the impact of family history of disease and hygienic habits on adolescents’ SRH in previous studies. These two variables have been considered in our study.
The family history of diseases did not associate to SRH linearly. However, its descending non-linear effect is shown in .
Similarly, hygienic habits in adolescents associated to SRH non-linearly. Its non-linear effect on SRH is ascending in its diagram.
Our study showed that boys and girls rated their health similarly and the gender variable did not associate to SRH. Previous study had different results about relation between SRH and gender. In the studies that gender had significant association to SRH; girls rated their health poorer.[10
Age and the grade of student did not have any impact on SRH. Our study is consistent with the study of Vinglis et al
. and study of Wade et al
] while inconsistent with the study of Vinglis and et al
. (2002), which indicated that age is a predictor of SRH.[10
In previous studies of adolescents, the effect of hypertension and cholesterol on adolescents SRH were not evaluated. However, a study on the middle-aged and elderly Chinese which examined the relationship between SRH and cardio-metabolic disease indicated that participants who had cardiovascular diseases, diabetes, hypertension and metabolic syndrome were more likely to have a poor SRH.[32
] In our study the average of blood pressure and total cholesterol did not have statistically a significant effect on SRH.
Furthermore, BMI in adolescents did not associate to SRH. However, Evelyn et al
. showed that adolescent with top quintile of BMI had lower health rating.[10
About nutrition habit, a longitudinal study on adults Danish indicated that poor dietary intake related to poor SRH. A US adolescents’ study showed that SRH status is not related to the overall quality of the adolescents’ diet. In our study, nutrition habits did not associate to SRH, so confirmed the US study.[23
Other variables that did not associate to SRH are family structure and school achievement. In other studies, it was found that students who had better family structure and family finance situation had better SRH[10
] and school achievement had a positive effect on high SRH.[10
Among the factors that seem to be related to adolescents’ SRH were mental dimensions such as stress, depression, and other mental problems. However, these factors were not measured in the case of adolescent concerning the national study, therefore, these factors were not considered in this study.