Recruitment and Sampling
Recruitment and sampling started in September 2011 with the publication of an EU press release and national press releases; the pilot study received press coverage in several countries.
Fourteen countries recruited in schools and three via the national population registers. The existence and accessibility of such registers differs from one EU country to another.
Different approaches were taken for recruiting volunteers, involving local communities and school directors, and including small educational gifts for children and/or mothers. A variety of means were used to collect information, including Computer Assisted Personal Interview (CAPI) systems.
The human biomonitoring (HBM) levels measured in the field of environmental health, aimed at assessing exposure of a wide population to a variety of agents, are usually low. This is contrast with the measurement of the exposure of workers to a specific known agent in a factory. To detect the sources of levels measured in the general population and understand possible interferences, it is crucial to collect the maximum amount of information through different questionnaires.
Five different questionnaires were collected
- Recruitment interview: for selecting participants and checking inclusion and exclusion criteria, with attention to external factors such as diseases that could disturb the objectives of the survey;
- Hair questionnaire: understanding sample collection and possible side effects, e.g. dying of hair can influence some results;
- Urine questionnaire: checking sample collection conditions, ascertaining that the sample can be used, e.g. there is a big difference between urine collected at first void and urine collected during the day;
- Basic questionnaire: collecting information on lifestyle, eating and smoking habits, socio-economic status, etc.;
- Non-responder questionnaire: assessing the representativeness of the sample population, e.g. we know that certain groups tend to be more willing to participate in such a survey.
Achievements during recruitment and sampling
- All countries collected hair and urine samples and completed questionnaires either at participants’ homes or at the children’s schools. Questionnaire data from 1 844 mother and child pairs were collected for the 4 basic chemicals and 621 for Bisphenol A.
- Initially, recruitment was meant to last until December 2011, but it was extended until the beginning of February 2012 as most countries had difficulties finding suitable volunteers. It was not easy to reach the requested numbers and age groups, partly due to the small size of the sampled population and taking into account that this was the first HBM study for many of the countries.
- The number of positive answers to invitations for participation varied also widely among countries. They are different possible explanations. For instance, in some countries the mother’s age when her first child was born is higher than in others meaning that it was difficult to find mothers below 45 old. In other countries, the parents’ ability to speak the language of the questionnaires was limited, etc.
- Computer Assisted Personal Interview (CAPI) systems were used but need to be improved for further upcoming studies. Taking into account budget constraints and easiness of development, a CAPI which needed an internet connection during the interview was ultimately chosen. Therefore many countries used a paper version of the questionnaire for the interviews, and then used CAPI only to input the data.