Childhood Obesity Surveillance Initiative (COSI) in Poland: Implementation of Two Rounds of the Study in the Context of International Methodological Assumptions

The COSI is a unique system consisting of systematic data collection, analysis, interpretation and dissemination of results to monitor an important public health problem, namely, excessive body weight in children. The system involves the weight and height measurements of primary school children aged 6–9 years.

The research involves applying a standardised methodology and conducting research based on strictly defined rules in each Member State, according to the international research protocol (19). Applying these rules results in delivering the relevant data and enables both the progress of the obesity epidemic to be tracked and inter-country comparisons to be made. Although individual countries can develop systems adapted to local conditions, surveys must be collected using a standardised methodology in accordance with the agreed joint protocol to provide relevant and comparable data (19). An international protocol is developed for each survey round. The protocol contains instructions about the mandatory and voluntary requirements for research preparation and conduct, as follows: the period of data collection, sampling strategy, population age and size within the national samples, research instruments and variables, translation procedures for questionnaires, method of conducting anthropometric measurements and the tools used for this purpose, training of examiners, data entry, data management and research ethics procedures. The basic principles of the COSI system in Member States recommend creating a simple national system and integrating it with other existing systems of health care, as well as anthropometric and dietary systems.

A mandatory objective for each round of data collection is to measure the following:

weight, height and body mass index (BMI);

Countries may extend the mandatory anthropometric measurements and use optional research tools and variables to measure and collect the following:

waist circumference and hip circumference;

Following the COSI protocol, measurements are carried out among primary school students. Countries can select one or more age groups from the following: 6.0–6.9, 7.0–7.9, 8.0–8.9 or 9.0–9.9. Children in Poland aged 8.0–8.9 years (the period between the eighth and ninth birthdays) were examined under the study in 2016 and 2018.

It is recommended that the national sample size is close to, or more than, 2,300 children per age group, selected from a minimum of 2,800 participating pupils.

Provinces in Poland were selected according to their sizes and economic development levels. Primary schools were randomly chosen from the database of primary schools available from the website of the Ministry of National Education in the list of schools and centres by type.

Education Information System (at Education IT Centre) – http://www.cie.men.gov.pl/index.php/sio-wykaz-szkol-i-placowek/27-wykaz-wg-typow.html; accessed: 8 September 2015.

A nationwide survey was carried out in November–December 2016 in 135 schools in nine provinces (37 poviats) of Poland. A group of 3,408 children from the 2nd and 3rd grades of primary school were examined. The final sample consisted of children for whom the completeness of data, in terms of the key variables, was confirmed: informed consent for participation, age, gender, height and body weight. Forms were completed by 2,298 parents (87% of the sample implementation).

The second round of study began in the final quarter of 2018 and was finished and filed at the end of the year. The survey sample was extended to 12 provinces (three provinces more than in the previous round of research). Survey was carried out in 140 schools. A group of 2691 pupils aged 8 years from the 2nd grade of primary schools were examined. Forms were completed by 2,450 parents (91% of the sample implementation).

The geographical distributions of the sample in COSI 2016 and 2018 are presented in Figures 1 and 2, respectively.

Figure 1

Figure 2

The COSI instruments comprise three types of questionnaires (forms) that are used to create the national survey:

mandatory instruments: (1) Child Record Form, completed by the examiner; and (2) School Record Form, completed by the school nurse or school director;

Variables used in the Polish COSI survey in 2016 included mandatory anthropometric measurements (weight, height and waist and hip circumferences), as well as data from measurements of diastolic and systolic blood pressure as national variables. The optional questionnaire for parents was also used, which included questions about, among other things, diseases occurring in the family, family lifestyle, as well as the child’s physical activity and eating behaviour. The particular thematic areas included in the forms are described in Table 2.

The tool translation process in the COSI programme followed the procedure specified by the WHO. According to these standards, all forms and research documentation used in the Polish COSI study (measurement protocol, school form and instructions, the form with the letter and the consent form for the parents and letters to the schools) were translated into Polish, following the indicated recommendations. Standard procedure included the following: forward translation, expert panel back-translation, pretesting and preparation of the final version of all documents in Polish.

Consent for the study was obtained from the Bioethics Commission at the Institute of Mother and Child in 2015

Opinion of the Bioethical Commission No. 22/2015 (22.11.2015).

Implementation of the COSI survey was carried out in cooperation with provincial coordinators and school nurses. The invited coordinators were team managers providing nursing care for students in schools.

A 2-day training programme was held in November 2016 for the provincial coordinators. The training was carried out by a Polish team from the Institute of Mother and Child and by representatives from the WHO office, with the participation of foreign experts. The thematic scope of the training covered, among other things, the main assumptions of the project and the methodology for anthropometric measurements, research tools and the tasks of the provincial coordinators and school nurses. Provincial coordinators supervised the correct implementation of COSI surveys in schools in their region. They were in constant contact with the examiners (school nurses) and helped them to solve emerging problems, answered questions, and in cases of doubt, contacted project coordinators at the Institute of Mother and Child.

The examiners were responsible for the following:

measurement of children’s anthropometric parameters (weight, height, as well as waist and hip circumferences) and also systolic and diastolic blood pressure;

Measurements were conducted by trained school nurses according to the COSI protocol procedures using standardised measurements. SECA 878 – mobile electronic scales were used, with coupled mobile stadiometer SECA 217 (Seca GmbH & Co.), which are recommended and meet the requirements of COSI procedures. Other type of measurement equipment was not specified in protocol. Centimetre tape and electronic sphygmomanometers using cuffs in sizes suitable for children aged 8 years (OMRON, different types, not specified), both from the schools nurse’s office, were used. Each measurement was performed twice, and the final value was the arithmetic mean of the two measurements. The result calculated in this way was entered by the nurse into the child’s measurement form.

The data from the received questionnaires were coded by a team from the Institute of Mother and Child, using the Open Clinica system (2016) or EpiData forms (2018). The 2016 database was prepared based on the WHO COSI Guidelines on Data Processing and Cleaning. The database was subjected to the verification procedure by the WHO Regional Office for Europe. The same procedure was implemented for the data 2019.

Following the COSI protocol, the criteria developed by WHO were applied to define overweight and obesity using key variables (weight and height). Cut-off points were used to calculate the BMI z-score appropriate for sex and age (BMI-for-age), in accordance with WHO 2007 recommendations (22), and the ‘WHO Anthro’ macro for SPSS was used for the calculations (23). BMI was calculated as a measure of the relative weight index. Overweight was defined as the percentage of children with BMI +1 standard deviation (SD) z-score, and obesity was defined as children having z-score above +2 SD. Such cut-off points corresponded to values of BMI = 17.7 kg/m² for boys and BMI = 18.0 kg/m² for girls in cases of overweight and BMI = 20.1 and 21.0 kg/m², respectively, in the case of obesity. The assessment was made in semi-annual age ranges.