| Definitions | Methodology | Publications | Links | Contact |
Age – age in full years at the time of measurement. The formula was used to calculate the student's age: (date of measurements – date of birth)/365.25.
Body mass index (BMI) – body mass divided by the square of height (kg/m2). Anthropometric measurements like body mass and height were taken in schools. These measurements are the basis for calculating BMI. The estimated weight of the clothes worn at the time was deducted from the 2015/16 and 2018/19 measured body mass results, according to the class and clothing category, a minimum of 100 g (underwear) and a maximum of 800 g (heavy clothes such as sweaters and jeans). Since the 2021/22 school year survey, the height of the student and the weight of the clothing corresponding to this height (<130 cm, 130–139 cm, etc. in 10 cm increments up to >180 cm) in different clothing categories have been taken into account when correcting body weight. To determine the average weight of the clothes, nearly 1,000 items were weighed to the nearest gram. For each garment of the same type, at least ten items were weighed in each body length range. The average weight was then calculated for each garment category: a minimum of 55 g (underwear) and a maximum of 1073 g (heavy garments such as sweaters and jeans).
BMI categories – underweight, normal weight, overweight, obesity. Two different methods are used to define BMI categories: the WHO (WHO 2007) and the IOTF (International Obesity Task Force) method (Cole et al. 2000, Cole et al. 2007).
In the case of the WHO method, the calculation of BMI is based on the student's gender and age, taking into account the standard deviation (SD) of the z-score to the nearest one month. BMI distributions of students according to WHO growth curves:
In the IOTF method, the BMI calculation is also based on the student's gender and age to the nearest one month, but the cut-off points are based on centiles, where they eventually align with adult BMI categories. The cut-off points for BMI categories for children, taking into account gender and age, are published on the World Obesity Federation website.
Excess body weight - overweight and obesity combined, WHO growth norm z-score distribution greater than 1 SD.
County - specified by the location of the school.
Number – the number of pupils who participated in the survey.
Percentile – in statistics, a k-th percentile (percentile score or centile) is a score below which a given percentage k of scores in its frequency distribution falls (exclusive definition) or a score at or below which a given percentage falls (inclusive definition). Example 1: For the 1st grade boys' body mass index in 2019, the 5th percentile shows that 5% of boys have a BMI lower than 13.8. Example 2: For the 1st grade boys' body mass index in 2019, the 95th percentile shows that 95% of boys have a BMI lower than 22.1 or, conversely, 5% of boys have a BMI higher than 22.1
Region – defined based on NUTS 3, a level of the Nomenclature of Territorial Units for Statistics (NUTS; French: Nomenclature des unités territoriales statistiques). NUTS is a standard for referencing subdivisions of the member countries of the European Union and it consists of a hierarchy of three levels: NUTS 1, 2 and 3, corresponding to the largest, medium and smallest subdivisions. In Estonia, NUTS 3 regions include the following counties:
Settlement unit – residence of the student at the time of the measurement.
European Childhood Obesity Surveillance Initiative or COSI is an initiative of the WHO Regional Office for Europe, which aims to prevent the growing obesity epidemic. Estonia joined the initiative in the academic year of 2015/16. More than 45 countries have joined this initiative. The main target group for monitoring is children aged 6.0–9.9 years, but other age groups may also be included. The collected data will be used to assess trends in overweight and obesity in order to gain a more accurate overview of the evolution of the epidemic and to develop intervention measures.
The data collected about the students are: body weight, height, hip and waist circumference and background data, including age, place of residence, eating breakfast on the morning of the study day. The data collected about the school environment include physical activity and sports opportunities during and after studies; food choices available to students at school; activities promoting healthy eating and lifestyle at school. Since the 2018/19 academic year survey, a family record form is additionally used to collect information about students' physical activity and eating habits, the family's socio-economic background and other factors related to the home environment.
2015/16 academic year study
In Estonia, the study sample for the academic year 2015/16 was made up of all first grade students of general education schools (n = 15,457) from 497 schools. Schools did not participate in the study if the management did not agree with it or where it was not possible to find a suitable time during the data collection period to carry out the measurements. In addition, some schools with a very small number of students located far from county centres, schools with English as the language of study, and some schools for students with special needs were also excluded from the sample. Students who were absent from school on the day of the study (n = 666), whose parents refused to the survey and measurements (n = 457) and students who themselves refused to participate in the study (n = 23) were not included in the study.
A total of 381 schools and 12,700 students (82.2% of the sample) participated in the survey. The tables present the data of 12,646 students [the data of 9-year-olds (n = 15) and those students whose anthropometric measurement results were extremely small or large (n = 39)] according to the 2007 WHO school-age and adolescent growth norms, have been removed. A z-score of less than -6 or greater than 5 SD for body mass, less than -6 and greater than 6 SD for height, and less than -5 and greater than 5 SD for BMI were considered extreme.
2018/19 academic year study
The initial sample was made up of schools that participated in the study in the academic year 2015/16. In this study, it was planned to include 50% of the schools that participated in the previous study. Since not many schools in Pärnu County participated in the 2015/16 academic year, more schools from Pärnu County were included this time in order to get a more representative overview. Although approximately twice as many Pärnu County schools participated in the study of the academic year 2018/19 than in the previous study, due to the shift of county borders as a result of the administrative reform in 2017, the number of students in the two waves of the study did not differ significantly. Schools that were closed in the meantime were replaced with schools from the same county which had as similar student numbers as possible. Schools that changed their name or joined another school were also included in the sample., schools that were transferred to another county after the 2017 administrative reform were not included in the sample. In addition, schools did not participate in the survey if the management did not agree to participate, if in 2018/19 the first grade was not opened or if it was not possible to find a suitable time for the measurements during the specified data collection period. Also, some of the schools of students with special educational needs withdrew from the survey.
Students who were absent from school on the day of the study (n = 1563), whose parents refused the survey and measurements (n = 566) and those students who did not want to participate in the study (n = 88) were excluded from the study. Other reasons for students not being measured included students with special needs, home or distance learning, as well as students who were out on the day of the measurement or who were not measured due to time constraints (n = 253). In the course of arranging the database, the data of 60 students was deleted. First, students were removed from the database whose record forms did not indicate date, sex, body weight or height (n = 32) and whose anthropometric measurements were extremely small or large according to the 2007 WHO’s school-aged and adolescent growth norms (n = 25 in the 1st grade, n = 25 in the 4th grade). A z-score of less than -6 or greater than 5 SD for body mass, less than -6 and greater than 6 SD for height, and less than -5 and greater than 5 SD for BMI were considered extreme. There were 6164 first grade and 6174 fourth grade students from 191 schools participating in the study.
2021/22 academic year study
In the academic year 2021/22, the initial sample consisted of 197 schools, but in order to achieve county representativeness and obtain the required number of students, 203 schools were included in the final sample. The goal was to retain as much of the sample as possible in the 2018/19 academic year. However, schools with special educational needs were excluded from the sample due to previous withdrawals or low participation rates. In addition to schools located far from the county centre with a small number of students, 12 very small schools where the total number of students in the first, fourth and seventh grades was ten or less were excluded from the selection, regardless of location. In order to maintain regional representativeness, in addition to the schools that participated in the 2018/19 academic year, first those that participated in the 2015/16 academic year and then, if necessary, schools that had not previously participated at all, were invited to the survey.
In the 203 schools that participated in the study, a total of 25,219 students studied in the first, fourth and seventh grades in the 2021/22 academic year (Estonian Education Information System, May 2022), forming the initial sample of students. Students who were absent from school on the day of the study (n = 3873), whose parents refused the survey and measurements (n = 904) and students who did not want to participate in the study (n = 254) were excluded from the study. Other reasons for students not being measured included, for example, students with special needs, home or distance learning, as well as students who were out on the day of the measurement or who were not measured due to time constraints (n = 1626). In the course of arranging the database, data were deleted if the student's date of birth, body weight or height were not indicated on the student's record form (n = 165), if the student was wearing a plaster cast, orthosis or other medical aid during the measurement (n = 37), if the student's age did not correspond to the typical age of the class under study ( 6-, 9-, 12-, 15- or 16-year-olds n = 354) and whose anthropometric measurements were extremely small or large according to WHO’s school-age and adolescent growth norms in 2007 (n = 36). A z-score of less than -6 or greater than 5 SD for body mass, less than -6 and greater than 6 SD for height, and less than -5 and greater than 5 SD for BMI were considered extreme. After cleaning the data, 17,969 students remained in the database: 6,042 students from the First grade, 6,200 students from the fourth grade, and 5,727 students from the seventh grade.
Gluškova N, Nelis L, Nurk E. Eesti õpilaste kasvu seire: 2018/19. õppeaasta uuringu raport. WHO Childhood Obesity Surveillance Initiative (COSI). Tallinn: National Insitute for Health Development; 2021. Report is available here in pdf-format (summary in English)
Metsoja A, Nelis L, Nurk E. WHO Childhood Obesity Surveillance Initiative (COSI): Estonian study report for the academic year 2015/2016. Tallinn: National Insitute for Health Development; 2018. Report is available here in pdf-format
Cole TJ, Bellizzi MC, Flegal KM, Dietz WH. Establishing a standard definition for child overweight and obesity worldwide: international survey. BMJ. 2000; 320:1240-1245.
Cole TJ, Flegal KM, Nicholls D, Jackson AA. Body mass index cut offs to define thinness in children and adolescents: international survey. BMJ. 2007; 335:194-201.
World Health Organization (2007). Growth Reference 5-19 years: BMI-for-age (5-19 years). URL: http://www.who.int/growthref/who2007_bmi_for_age/en/ (10.01.2018).
World Obesity Federation. Obesity Classification. URL: https://www.worldobesity.org/about/about-obesity/obesity-classification.
Natalja Pajula
Department of Research Data Management
National Institute for Health Development
E-mail: Natalja.Pajula@tai.ee
Eha Nurk
Science Centre
National Institute for Health Development
E-mail: Eha.Nurk@tai.ee
Updated: 4.01.2024