Abstract

Objective:

To estimate the prevalence of moderate and vigorous physical activity (MVPA), as defined by the World Health Organisation (WHO), and associated factors among teenagers from Barcelona in 2012.

Methods:

Cross-sectional survey to assess risk factors in a representative sample of secondary school students (aged 13-16 years, International Standard Classification of Education [ISCED] 2, n = 2,162; and 17-18 years, ISCED 3, n = 1016) in Barcelona. We estimated MVPA prevalence overall, and for each independent variable and each gender. Poisson regression models with robust variance were fit to examine the factors associated with high-level MVPA, and obtained prevalence ratios (PR) and 95% confidence intervals (95%CI).

Results:

Only 13% of ISCED 2 and 10% of ISCED 3 students met the WHO physical activity recommendations. This percentage was lower among girls at both academic levels. MVPA was lower among ISCED 3 compared to ISCED 2 students, and among students with a lower socioeconomic status. Physical activity was associated with positive self-perception of the health status (e.g., positive self-perception of health status among ISCED 2 compared to ISCED 3 students: PR = 1.31 [95%CI: 1.22-1.41] and 1.61 [95%CI: 1.44-1.81] for boys and girls, respectively].

Conclusions:

The percentage of teenagers who met WHO MVPA recommendations was low. Strategies are needed to increase MVPA levels, particularly in older girls, and students from low socioeconomic backgrounds.

Keywords:
Exercise; Adolescence; Gender identity; Health survey; Cross-sectional studies

Resumen

Objetivo:

Estimar la prevalencia de actividad física moderada y vigorosa (AFMV), tal como la define la Organización Mundial de la Salud (OMS), y sus factores asociados en adolescentes de Barcelona en el año 2012.

Métodos:

Encuesta transversal para evaluar los factores de riesgo en una muestra representativa de estudiantes de secundaria (13-16 años, Clasificación Internacional Normalizada de la Educación [CINE] 2, n = 2162; y 17-18 años, CINE 3, n = 1016) de Barcelona. Se estimó la prevalencia de la AFMV en general y para cada variable independiente y sexo. Se ajustaron modelos de regresión con varianza robusta para examinar los factores asociados con niveles altos de AFMV, obteniendo razones de prevalencia (RP) y los intervalos de confianza del 95% (IC95%).

Resultados:

Solo el 13% de los estudiantes de CINE 2 y el 10% de CINE 3 cumplían con las recomendaciones de actividad física de la OMS. Este porcentaje fue inferior en las chicas en ambos niveles académicos. La AFMV fue menor en los estudiantes de CINE 3 comparados con los de CINE 2, y en aquellos con un nivel socioeconómico más bajo. La actividad física se asoció con una autopercepción positiva del estado de salud (p. ej., autopercepción positiva de la salud en los/las estudiantes de CINE 2, en comparación con los/las de CINE 3: PR = 1,31 [IC95%: 1,22-1,41] y 1,61 [IC95%: 1,44-1,81] para chicos y chicas, respectivamente).

Conclusiones:

El porcentaje de adolescentes que cumplían con las recomendaciones de AFMV de la OMS fue bajo. Se necesitan estrategias para incrementar la AFMV, en particular en las chicas de mayor edad y en los/las estudiantes con niveles socioeconómicos bajos.

Palabras clave:
Ejercicio; Adolescencia; Identidad de género; Encuesta de salud; Estudios transversales

Introduction

Regular vigorous physical activity contributes to improved general physical health and lower rates of depression and anxiety.¹1. Ahn S, Fedewa AL. A meta-analysis of the relationship between children's physical activity and mental health. J Pediatr Psychol. 2011;36:385-97. Research suggests that academic performance is also enhanced in students who regularly engage in physical activity.²2. Biddle SJH, Asare M. Physical activity and mental health in children and adolescents: a review of reviews. Br J Sports Med. 2011;45:886-95. Importantly, from a long-term health perspective, participation in regular physical activity during adolescence is associated with a greater probability of being a physically active adult, a key determinant in preventing a range of negative health outcomes.³3. Hallal PC, Victora CG, Azevedo MR, et al. Adolescent physical activity and health: a systematic review. Sports Med Auckl NZ. 2006;36:1019-30.

The World Health Organisation (WHO) recommends that children and teenagers aged 5-17 years participate in at least 60minutes of moderate or vigorous physical activity (MVPA) daily. MVPA is associated with more favourable health parameters, such as lower central adiposity, reduced cardiovascular risk and improved bone health.⁴4. WHO. Global recommendations on physical activity for health. Geneva, Switzerland: World Health Organization; 2010. However, most studies in teenagers indicate that only a small percentage meet these recommendations. Global estimates suggest that only 20% of teenagers aged 13-15 years achieve recommended levels of MVPA.⁵5. Hallal PC, Andersen LB, Bull FC, et al. Global physical activity levels: surveillance progress, pitfalls, and prospects. Lancet. 2012;380:247-57. In Europe, this percentage is 34% among 11- to 15-year-olds,⁶6. Cavill N, Kahlmeier S, Racioppi F. Physical activity and health in Europe: evidence for action. Copenhagen, Denmark: World Health Organization; 2006. and just 17% in Spain.⁷7. Currie C, Gabhainn SN, Godeau E, et al. Inequalities in young people's health: HBSC international report from the 2005/2006 survey. Copenhagen, Denmark: World Health Organization; 2008. In 2008, in Barcelona, it is estimated that less than half (44%) of students aged 13 to 19 years regularly participated in physical activity, and there is no information regarding the amount of time spent in physical activity.⁸8. García-Continente X, Pérez-Giménez A, Espelt A, et al. Factors associated with media use among adolescents: a multilevel approach. Eur J Public Health. 2014;24:5-10.

Regular physical activity during adolescence appears to be especially uncommon among girls,⁹9. Devís-Devís J, Peiró-Velert C, Beltrán-Carrillo VJ, et al. Brief report: association between socio-demographic factors, screen media usage and physical activity by type of day in Spanish adolescents. J Adolesc. 2012;35:213-8. older teenagers,¹⁰10. Colley RC, Garriguet D, Janssen I, et al. Physical activity of Canadian children and youth: accelerometer results from the 2007 to 2009 Canadian Health Measures Survey. Health Rep. 2011;22:15-23. and those with a lower socioeconomic status (SES).¹¹11. Stalsberg R, Pedersen AV. Effects of socioeconomic status on the physical activity in adolescents: a systematic review of the evidence. Scand J Med Sci Sports. 2010;20:368-83. Lifestyle factors, such as alcohol or tobacco use,¹²12. Halperin AC, Smith SS, Heiligenstein E, et al. Cigarette smoking and associated health risks among students at five universities. Nicotine Tob Res. 2010;12:96-104. and some health indicators, such as self-perceived health status, mood or body mass index (BMI),¹³13. Iannotti R, Janssen I, Haug E, et al. Interrelationships of adolescent physical activity, screen-based sedentary behaviour, and social and psychological health. Int J Public Health. 2009;54:191-8. have also been found to be related physical activity in teenagers. However, the reported strength and the direction of these associations are often contradictory, possibly because few studies have accounted for important factors such as school and neighbourhood settings, and other factors that may limit physical activity.¹⁴14. Galán I, Boix R, Medrano MJ, et al. Individual factors and school-based policies related to adherence to physical activity recommendations in Spanish adolescents. Prev Sci. 2014;15:588-99.^,1515. Franzini L, Elliott MN, Cuccaro P, et al. Influences of physical and social neighborhood environments on children's physical activity and obesity. Am J Public Health. 2009;99:271-8. Moreover, parents, friends and teachers have an important influence on physical activity, and their support is associated with greater participation in physical activity.¹⁶16. De Meester F, van Lenthe FJ, Spittaels H, et al. Interventions for promoting physical activity among European teenagers: a systematic review. Int J Behav Nutr Phys Act. 2009;6:82.

Given the importance of physical activity for health and wellbeing, and the current climate of poor compliance with recommended levels of physical activity among teenagers, it is important to identify factors associated with failure to achieve MVPA recommendations.⁴4. WHO. Global recommendations on physical activity for health. Geneva, Switzerland: World Health Organization; 2010. This would facilitate the design of interventions to address factors that prevent teenagers from achieving recommended MVPA levels. Thus, the aim of our study was to estimate the prevalence of moderate and vigorous physical activity (MVPA), as defined by the WHO, and associated factors among teenagers from Barcelona in 2012.

Methods

A cross-sectional survey of lifestyle risk factors (Risk Factors in Secondary School Students;FRESC) was conducted in a representative sample of secondary school students from Barcelona who had been classified according to the UNESCO International Standard Classification of Education (ISCED) as ISCED 2 (13-16 years) and ISCED 3 (17-18 years).¹⁷17. UNESCO. ISCED. International Standard Classification of Education 2011. Montreal, Canada: UNESCO Institute for Statistics; 2012. Students completed an anonymous self-report questionnaire that collected information on various behaviours, such as substance use, leisure time activities, and sedentary behaviour. Anthropometric data based objective measurements of weight and height was also collected.

In Barcelona, in 2011-2012, there were 274 schools, 1,659 classrooms and 40,278 students.¹⁸18. Ajuntament de Barcelona [Internet]. Anuaris estadístics de la ciutat de Barcelona. [Accessed 15/09/2016]. Available at: http://www.bcn.cat/estadistica/catala/dades/anuaris/anuari13/cap05/
http://www.bcn.cat/estadistica/catala/da... Stratified random sampling was used for all academic levels, with the classroom as the smallest sampling unit. Stratification was conducted according to type of school (public, private or subsidised) and the SES of the surrounding neighbourhood (low, medium or high, according to the Index of Familial Economic Capacity).¹⁹19. Santigosa A. La capacitat econòmica i familiar a la ciutat de Barcelona, 1988-1996. Barc Soc. 2002:21-9. The students’ response rate was 87.6%. Students who provided incomplete data (9%) were excluded from the study, resulted in a total sample of 3,178 students (ISCED 2, n = 2,162; ISCED 3, n = 1,016; girls, n = 1,643; boys, n = 1,535).

The self-reported questionnaire²⁰20. Agència de Salut Pública de Barcelona [Internet]. Enquesta de Factors de Risc a l'Escola Secundària (FRESC). [Accessed 15/09/2016]. Available at: http://www.aspb.cat/arees/la-salut-en-xifres/enquesta-fresc/
http://www.aspb.cat/arees/la-salut-en-xi... was administered between January and March of 2012 by trained personnel from Barcelona Public Health Agency (ASPB) during school time in the presence of the classroom teacher. Principals and teachers of selected schools were properly informed about the objectives of the study and they gave their verbal informed consent. Given the nature of the questionnaire, the Research Committee of the ASPB did not consider necessary a parental informed consent.

The dataset was created by scanning the completed forms using the Teleform 10.2 program.

Dependent variable

The dependent variable was based on answers to the question: “How many hours a day do you spend practising sport? (i.e. physical activity that makes you sweat and become out of breath, such as, football, swimming, etc., including physical activity practised at school)”. We requested a separate response to this open question for each day of the week, which allowed us to assess the daily number of minutes of physical activity. From this we determined whether students had performed more than 60minutes or less than 60minutes of physical activity per day, and constructed three distinct dependent variables:

Independent variables

We used three types of independent variables (Table 1):

Statistical analysis

All analyses were stratified by sex. A preliminary univariate analysis was conducted to establish the percentage of teenagers who participated in MVPA for ≥1hour on ≥3 (MVPA3), ≥5 (MVPA5), or 7 (MVPA7) days/week, for each sex and academic level. To evaluate which factors were associated with greater levels of MVPA, we fit crude and adjusted Poisson regression models with robust variance, obtaining prevalence ratios (PR) and 95% confidence intervals (95%CI)²³23. Espelt A, Mari-Dell'Olmo M, Penelo E, et al. Applied prevalence ratio estimation with different regression models: an example from a cross-national study on substance use research. Adicciones. 2016:2016.. We used the MVPA3 variable to study associated factors, since there were too few cases of MVPA5 and MVPA7. A sensitivity analysis was also carried out to evaluate the consistency of the result across all three MVPA variables. All analyses were conducted using STATA 13.

Results

Just under half (48.3%) of the sample were boys, 23.9% were 1st or 2nd generation immigrants, and 88.8% were from a medium or high SES background. Almost one-quarter (24.9%) of students were overweight or obese, 6.3% of boys and 18.9% of girls reported being on diet at the time of the interview, and approximately two-thirds (60.2%) reported screen-related sedentary behaviour (Table 1).

Figure 1 shows the percentage of students that practised MVPA, according to each variable (MVPA3, MVPA5 and MVPA7). In all cases, the percentage of students that practised MVPA was higher among boys than girls and among ISCED 2 students. For example, while 13.3% of all ISCED 2 students reported practising MVPA7, the percentage among boys was 3 times that among girls (20% and 7%, respectively). The percentage of ISCED 3 students who met the recommended levels of activity (MVPA7) was lower (10.3%), but still higher among boys than girls (16% and 5%, respectively).

Table 2 shows the crude and adjusted PR for each sex. In both sexes, the prevalence of MVPA3 was higher among more junior students (ISCED 2), those from families with higher SES, and those who reported excellent or very good self-perceived health status. For example, the PR of MVPA3 in ISCED 2 compared to ISCED 3 students was 1.31 (95%CI: 1.22-1.41) and 1.61 (95%CI: 1.44-1.81) among boys and girls, respectively. Among girls but not boys, MVPA3 was also associated with being native (PR = 1.23; 95% CI: 1.06-1.43; compared to 1^st generation immigrants), being on a diet (PR = 1.14; 95%CI: 1.03-1.26), not reporting screen-related sedentary behaviours, and having a good self-perceived academic level relative to classmates. Neither tobacco nor cannabis use were significantly associated with MVPA after adjustment for the other independent variables. Finally, our sensitivity analysis did not reveal remarkable differences between the results for the final models using MPVA5 and MPVA7 (results not shown).

Discussion

Our results show that only 12% of students in Barcelona in 2012 met the WHO recommendations for MVPA. MVPA was considerably lower among girls and also among ISCED 3 students, suggesting a decrease in MVPA related to aging. We found that MPVA was positively associated with SES and self-perceived health status.

Less than one-eighth of students achieved the WHO-recommended levels MVPA (12%), which is consistent with some national and international studies,⁷7. Currie C, Gabhainn SN, Godeau E, et al. Inequalities in young people's health: HBSC international report from the 2005/2006 survey. Copenhagen, Denmark: World Health Organization; 2008.^,1010. Colley RC, Garriguet D, Janssen I, et al. Physical activity of Canadian children and youth: accelerometer results from the 2007 to 2009 Canadian Health Measures Survey. Health Rep. 2011;22:15-23.^,2424. Martínez-Gómez D, Welk GJ, Calle ME, et al. Preliminary evidence of physical activity levels measured by accelerometer in Spanish adolescents: the AFINOS Study. Nutr Hosp. 2009;24:226-32. although other authors have reported MVPA rates of 50-70%.²⁴24. Martínez-Gómez D, Welk GJ, Calle ME, et al. Preliminary evidence of physical activity levels measured by accelerometer in Spanish adolescents: the AFINOS Study. Nutr Hosp. 2009;24:226-32.

25. Butcher K, Sallis JF, Mayer JA, et al. Correlates of physical activity guideline compliance for adolescents in 100 U.S. cities. J Adolesc Health. 2008;42: 360-8.^-2626. Roman B, Serra-Majem L, Ribas-Barba L, et al. How many children and adolescents in Spain comply with the recommendations on physical activity? J Sports Med Phys Fitness. 2008;48:380-7. Such disparities may be due to a number of reasons. First, some studies use less stringent MVPA recommendations than this study (WHO recommendations). Second, research using accelerometers to determine MVPA levels appear to overestimate MVPA because they record incidental lower intensity exercise. Finally, some studies include low intensity forms of physical activity, such as walking.²⁴24. Martínez-Gómez D, Welk GJ, Calle ME, et al. Preliminary evidence of physical activity levels measured by accelerometer in Spanish adolescents: the AFINOS Study. Nutr Hosp. 2009;24:226-32.^,2626. Roman B, Serra-Majem L, Ribas-Barba L, et al. How many children and adolescents in Spain comply with the recommendations on physical activity? J Sports Med Phys Fitness. 2008;48:380-7.

In line with previous research,²⁵25. Butcher K, Sallis JF, Mayer JA, et al. Correlates of physical activity guideline compliance for adolescents in 100 U.S. cities. J Adolesc Health. 2008;42: 360-8. we observed gender differences in MVPA levels, with boys reporting higher rates, both at ISCED 2 and ISCED 3. These differences may be because boys’ perceive fewer barriers to practising physical activity, and have more options for participation in sport, at both the school and leisure time.²⁷27. Amado-Alonso D, Leo-Marcos FM, Sánchez-Oliva D, et al. It is compatible the sport in scholar age with other social roles? A study through self-determination theory. RETOS. 2012:50-2. In addition, boys and girls practise activities of different intensity, the latter generally practising lower intensity activities.⁹9. Devís-Devís J, Peiró-Velert C, Beltrán-Carrillo VJ, et al. Brief report: association between socio-demographic factors, screen media usage and physical activity by type of day in Spanish adolescents. J Adolesc. 2012;35:213-8.^,1414. Galán I, Boix R, Medrano MJ, et al. Individual factors and school-based policies related to adherence to physical activity recommendations in Spanish adolescents. Prev Sci. 2014;15:588-99.

The most notable result is the decrease in MVPA between ISCED 2 and ISCED 3 in both sexes, although the decrease was more pronounced in girls. In our context, the strongest contributor to this decrease is probably the removal of compulsory physical activity from the school curriculum (physical education is compulsory in ISCED 2 but not in ISCED 3).¹⁴14. Galán I, Boix R, Medrano MJ, et al. Individual factors and school-based policies related to adherence to physical activity recommendations in Spanish adolescents. Prev Sci. 2014;15:588-99. Other authors have suggested that the transition from ISCED 2 to ISCED 3 involves more study time and screen use, such that ISCED 3 students have less time for physical activity.¹⁰10. Colley RC, Garriguet D, Janssen I, et al. Physical activity of Canadian children and youth: accelerometer results from the 2007 to 2009 Canadian Health Measures Survey. Health Rep. 2011;22:15-23.^,1414. Galán I, Boix R, Medrano MJ, et al. Individual factors and school-based policies related to adherence to physical activity recommendations in Spanish adolescents. Prev Sci. 2014;15:588-99. Decreased MVPA may also be due to girls’ biological maturation, which occurs around the time of transition to ISCED 3, and has been found to be related to lower participation in physical activities²⁸28. Eisenmann JC, Wickel EE. The biological basis of physical activity in children: revisited. Pediatr Exerc Sci. 2009;21:257-72.. Some studies have shown that the differences between sexes disappear after a adjustment for biological age.²⁸28. Eisenmann JC, Wickel EE. The biological basis of physical activity in children: revisited. Pediatr Exerc Sci. 2009;21:257-72.^,2929. Erlandson MC, Sherar LB, Mosewich AD, et al. Does controlling for biological maturity improve physical activity tracking? Med Sci Sports Exerc. 2011;43:800-7.

Individual SES was also related to MVPA in both sexes, in that individuals with higher SES were more likely to meet MVPA recommendations. A recent review shows similar results, with higher SES associated with greater physical activity in 58% of studies.¹¹11. Stalsberg R, Pedersen AV. Effects of socioeconomic status on the physical activity in adolescents: a systematic review of the evidence. Scand J Med Sci Sports. 2010;20:368-83. These differences could be because more disadvantaged families have generally lower paid jobs and poorer labour conditions, and teenagers from these households have to spend more of their free time doing housework or part time work, diminishing their availability to practise physical activity. Moreover, parents with poorer labour conditions may lead their children to be less active through their influence as role models.³⁰30. Dobbins M, De Corby K, Robeson P, et al. School-based physical activity programs for promoting physical activity and fitness in children and adolescents aged 6-18. Cochrane Database Syst Rev. 2009:CD007651. Additionally, those from lower SES backgrounds are likely to live in neighbourhoods and communities where parks and recreational facilities are less common or of a lower quality than those in more affluent neighbourhoods.⁶6. Cavill N, Kahlmeier S, Racioppi F. Physical activity and health in Europe: evidence for action. Copenhagen, Denmark: World Health Organization; 2006. Poorer awareness of the benefits of physical activity among families with lower SES could also explain these observed differences.¹¹11. Stalsberg R, Pedersen AV. Effects of socioeconomic status on the physical activity in adolescents: a systematic review of the evidence. Scand J Med Sci Sports. 2010;20:368-83. In addition, we found an association between MVPA and immigration status among girls. First and second generation immigrant girls may belong to families with a distinct gender concept, where girls could have a more traditional role and may practise less physical activity.³¹31. Gualdi-Russo E, Zaccagni L, Manzon VS, et al. Obesity and physical activity in children of immigrants. Eur J Public Health. 2014;24 Suppl 1:40-6. Nonetheless, more research is needed to explore the effect of country of origin on physical activity.

In terms of health-related variables, we found a positive relationship between self-perceived health status and MVPA levels in both sexes. This is consistent with previous studies indicating that physically active teenagers are more likely to have a positive perception of their health status than less active teenagers.³²32. Farias-Júnior JC, Lopes A, Mota J, et al. Physical activity practice and associated factors in adolescents in Northeastern Brazil. Rev Saúde Pública. 2012;46:505-15.^,3333. Aarnio M, Winter T, Kujala U, et al. Associations of health related behaviour, social relationships, and health status with persistent physical activity and inactivity: a study of Finnish adolescent twins. Br J Sports Med. 2002;36:360-4. This finding suggests that MVPA has a positive effect on teenagers’ health.¹1. Ahn S, Fedewa AL. A meta-analysis of the relationship between children's physical activity and mental health. J Pediatr Psychol. 2011;36:385-97. Unlike other studies, we did not observe an association between MVPA and cannabis or tobacco use,¹³13. Iannotti R, Janssen I, Haug E, et al. Interrelationships of adolescent physical activity, screen-based sedentary behaviour, and social and psychological health. Int J Public Health. 2009;54:191-8.^,3434. Kaczynski AT, Manske SR, Mannell RC, et al. Smoking and physical activity: a systematic review. Am J Health Behav. 2008;32:93-110. perhaps because some studies indicate that the relationship is only seen in those adolescents who practice high intensity activities.³⁴34. Kaczynski AT, Manske SR, Mannell RC, et al. Smoking and physical activity: a systematic review. Am J Health Behav. 2008;32:93-110.

Regarding the limitations of the present study, most data in this study are self-reported, except for the anthropometric measurements and the school-related variables. Although the objective measures are generally considered more robust, anonymous questionnaires on physical activity have been shown to have good validity and reliability, and remain a valuable tool for estimating levels of physical activity.³⁵35. Hagströmer M, Bergman P, De Bourdeaudhuij I, et al. Concurrent validity of a modified version of the International Physical Activity Questionnaire (IPAQ-A) in European adolescents: the HELENA Study. Int J Obes. 2008;32 Suppl 5: 42-8. Another limitation of this study could be the definition of physical activity used (practising MVPA for ≥1hour/day on ≥3 days/week) because there is no consensus on how to study physical activity using self-reported variables.³⁶36. Lowry R, Lee SM, Fulton JE, et al. Obesity and other correlates of physical activity and sedentary behaviors among US high school students. J Obes. 2013;2013:276318. Furthermore, our sensitivity analysis did not highlight remarkable differences between the results obtained using different MVPA variables. Finally, this study used a cross-sectional design, which allows us only to observe associations between variables, but not to infer causality in the observed relations.

In conclusion, this is the first study to analyse the WHO-recommended levels of MVPA and associated variables using a large representative sample of teenage students (13-18 years) from Barcelona city. The low levels of MVPA observed in this study, as defined by the WHO, suggest that an effort is needed to promote and/or to remove potential barriers to physical activity among adolescents, and this should be a public health priority. This study suggests that efforts to increase MVPA need to address gender and SES disparities, which appear to have a strong influence on MVPA. Additionally, policy makers should consider making physical activity part of the compulsory curriculum for ISCED 3 students.

The school setting is one of the most obvious places to target improvement in physical activity, since it provides the facilities, curriculum (including extra-curricular activities), policies and setting for students to participate in MVPA, independent of their SES.³⁰30. Dobbins M, De Corby K, Robeson P, et al. School-based physical activity programs for promoting physical activity and fitness in children and adolescents aged 6-18. Cochrane Database Syst Rev. 2009:CD007651. For this reason re-orienting education and health policy to incorporate physical activity and associated resources in the school setting, particularly for ISCED 3 students, should be considered. Finally, it would be interesting to conduct a study to know the reasons for the socioeconomic inequalities in physical activity in the adolescents of Barcelona, taking special attention to what happens during the changes between educational programs and with extracurricular activities.

Acknowledgments

The authors wish to thank the teachers, students and schools that participated in the study. We also thank the staff from the Community Health Service and the Evaluation and Intervention Methods Service at Barcelona Public Health Agency, who collaborated on this project. This research article represents partial fulfilment of the requirements for a Masters of Public Health for Alícia Ruiz Traserra, University of Pompeu Fabra, Barcelona.

References

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