The current findings showed that the level of happiness was not lower in the slums than among all Iranians [19]. Happiness was not different in men compared to women. Lower levels of happiness were observed in elderly, illiterate, unemployed, and separated people. Job satisfaction, life satisfaction, hope, social support, and sufficient income to cover living expenses were positively correlated with the happiness score.
In this study, the mean score of happiness in a slum area of Shiraz (Sang Siah) was 6.41. The mean score of Iranian happiness was reported to be 5.08 in 1997 [19]. In the 2017 World Happiness Report, Iran was ranked 108th with a score of 4.69 [9]. The World Happiness Score may not accurately reflect the population’s social well-being and happiness. Nationwide or citywide studies are needed to better understand the city or nation’s well-being. According to the theory of adaptation, having recently repeated negative stimuli, such as the effects of the economic sanctions on Iran, plays an important role in understanding happiness and social well-being and can result in different perceptions of good living standards by different people [20].
In this study, happiness was higher in single and married participants than in separated, divorced, or widowed ones. However, in a cross-national study on 39,082 participants from 29 Asian countries, it was determined that married participants were happier than single ones [21]. A longitudinal study by Stutzer reported that happier single people get married sooner than other groups and that married people are not happier than single ones [22]. Divorce or death of a spouse is correlated with psychological distress [23] and hopelessness [24]. In Iranian culture, divorce is unpopular and makes one vulnerable [25], and it could be the cause of unhappiness.
It was also determined that with an increase in job satisfaction, happiness scores increased, and unemployed participants had the lowest level of happiness. Some studies have shown that job satisfaction is a more important factor for happiness than having a job [26, 27]. Although Clark mentioned that unemployment had a greater effect on one’s well-being than financial satisfaction with one’s job [28], the current study shows that both employment and job satisfaction are among the important factors for well-being. Clark argues that in a region with a high rate of unemployment, people notice many other jobless people and therefore, they do not blame themselves for being unemployed, and having no job has a lesser effect on their wellbeing [28].
The results showed that people with no social support had lower scores of happiness. This is in line with the results of Hart et al. on 6037 participants in a SPOTLIGHT survey with a large social network in which trusted neighbors were correlated with higher levels of happiness [29]. In another study on South Korean university students, happiness was correlated with their perception of social support [30].
In the slums of Calcutta, social well-being was lower than the other groups compared, but it was higher than expected due to strong social relationships [15]. Another study in Nicaragua showed negative subjective well-being in people living in marginalized urban areas, and the most predictive factors affecting subjective well-being were objective income and social support [31].
The current results showed that life satisfaction is significantly correlated with happiness. Other studies have shown that these two variables are different in concept. Happiness depends on country characteristics and people living in a stable relationship, but life satisfaction is related to country of living and feelings of control [32].
Hope for the future had a positive correlation with happiness and could be predicted in this study. Other investigators have shown that happiness and hope are correlated with each other, but this correlation is not positive in all studies; some investigators have demonstrated a negative association between happiness and hope [33]. In a study on university students, however, a positive correlation between hope and subjective well-being was demonstrated [34].
Cigarette smokers were less happy than non-smokers in Sang Siah neighborhood, but in the presence of other factors, cigarette smoking was not correlated with happiness. This means that confounders such as socioeconomic factors affect this relation. A study on smoking status and happiness in nine countries of the former Soviet Union (fSU) showed that ex-smokers were happier than smokers [35].
According to the current results, opium-addicted participants were happier than others, probably due to mood changes in opium users [36]. However, this could be related to the dose and duration of consumption, which was not evaluated in this study. Happiness did not differ between participants consuming and those not consuming alcohol. It seems that the relationship between happiness and alcohol consumption is related to the type of alcohol and the culture of the people [37].
The current results indicated that 11.9 % of the participants had been subjected to violence. In a systematic review in Iran, the prevalence of domestic violence was reported to fluctuate between 5.4 and 94.7 % [38]. Participants who faced violence at home or in the neighborhood were less happy than others. The current results agree with the findings of the study which evaluated contextual correlates of happiness in European adults that feeling safety in a neighborhood was associated with higher levels of happiness [29]. A review of domestic violence in Iran showed that violence causes physical and mental problems and results in one member leaving the family [39]. A study in Mexico reported that intimate partner violence has a significant impact on happiness and well-being [40]. The association between happiness and violence could be explained by common determinants of violence and life satisfaction [41].
People with higher income satisfaction were happier, although income had no direct correlation with happiness in the current study, which is in agreement with another investigation [42]. Happiness depends on the distribution of income in the community and satisfaction with it in comparison with that of others [43]. Income and happiness have a weak relationship, but the concept of income satisfaction could affect happiness, which is justifiable by the conceptual-referent theory of happiness [44].
A positive correlation between mental and physical health was seen in Sang Siah. Many studies have shown that physical and mental health are important factors which are associated with happiness [45]. Veenhoven says happiness could protect people against being ill, and mental and physical health affect each other [46]. In some studies of younger adults, however, no significant correlation between physical health and happiness was detected.
Nevertheless, mental health had a strong association with happiness [47].
Religious people were happier than others not only in the current study but also in many others [45]. Religious beliefs give a sense of purpose to life [48] and provide the conditions for individuals to feel connected to an infinite source of power in times of unpleasant life experiences, fear, and sorrow [49].
The results of the current study show policy-makers that despite the economic problems caused by the sanctions against Iran, communities can be healthy and happy with the implementation of interventions to improve social support and strengthen familial foundations and safety in society, reduce violence, and increase job satisfaction and hope for the future (Additional file 2).