Definition of study aim and hypothesis This protocol and methodology were used in Kaunas pilot study, which aimed to analyse whether any environmental and social differences exist between the citizens' risk of hypertension, seeking to answer the study participants’ formulated question: “Why do citizens in my district suffer from hypertension more often than those in other ones?” To test the scientific hypothesis that the difference in the effect of the social environment on hypertension were mediated by exposure to urban built environment and green spaces exposure, the cross-sectional study was planned and defined in the research protocol. The study participants' activities have been created by the Kaunas pilot study scientific team together with citizens to conduct participatory action research and to evaluate the impacts on environmental education.

Writing the research protocol The protocol included all the activities needed for the data collection and statistical analysis for the scientific hypothesis testing in the Kaunas pilot. The study modelled environmental exposure to traffic emissions and objectively measured exposure to green space by estimating normalized difference vegetation index (NDVI) for every participant’s home address. Some of the information described in the protocol was the way of collecting personal environmental quality perception and self-reported health data, and analyzing traffic flows and green spaces data linked to each participant’s place of residence, personal socio-demographic and health-related data, and physical activity measurements by using the sensor Fitbit Alta. Also, it was defined how should be estimated the learning and empowerment of the participants by evaluating the impact of new knowledge on a better understanding of the links between environmental quality, physical activity, and health; on gained new practical skills in data collection and interpretation; on project contribution to facilitating personal changes in behaviours; and the contribution to a better understanding of the scientific topic.

Research protocol approval The study was conducted in accordance with the World Medical Association declaration of Helsinki: Ethical principles for medical research involving human. https://www.wma.net/policies-post/wma-declaration-of-helsinki-ethical-principles-for-medical-research-involving-human-subjects/ The protocol, the questionnaires, and the consent procedure were approved by the Kaunas Regional Committee for Biomedical Research Ethics. The citizens’ engagement, participants' activities, data analysis methods, and hypothesis testing methods were also approved by international reviewers during the study results publications in peer-review international scientific open access journals.

Usage of the research protocol All research activities defined by this protocol for hypothesis testing and the results from Kaunas citizen science project are detailed described in the articles published in the international peer-review scientific journals. The research findings are important for showing the citizen science possibility to contribute to evidence-based science and for motivating active participants. See below open access links to the Kaunas pilot study articles of practical usage the research protocol:
https://doi.org/10.3390/ijerph17207696
https://doi.org/10.3390/ijerph17124420
https://doi.org/10.3390/ijerph18116126
https://doi.org/10.3390/su13169368