Table 1.

Classification system for categorizing the Facebook posts

1. Overall topic: health Does the post relate to a health issue, or any other aspect (e.g. premiums, job descriptions)?	A. Yes B. No
2. Targeted disease /condition	A. unspecific, general health B. specific disease / condition   a. cardiovascular   b. orthopaedic/musculoskeletal   c. infectious diseases   d. cancer   e. mental diseases / mental health   f. pregnancy   g. type 2 diabetes
3. Lifestyle / behaviour The behaviour that is explained, illustrated, or promoted in the post	A. healthy nutrition B. exercise / physical activity C. stress and anxiety relief, relaxation D. dental / oral hygiene E. legal drugs (reducing / quitting / avoiding) F. protection from solar UV radiation and heat G. hygiene, prevention of infections, safer sex H. vaccination I. cancer screening J. safety at home / road safety / injury prevention
4. Type of information / communication The way the behaviour / disease is addressed in written form	A. appeal, invitation (to change behaviour) B. detailed information, educational content C. event notice (e.g. invitation to attend specific courses) D. prize game, contest, quiz
5. Preventive activity What is the type of preventive activity that the post asks the user to take part in – online or offline?	A. online information / education (to be read by user)/ prize game (to be executed online) B. offline educational event, health-related courses C. offline training, fitness courses D. phone hotline (giving background information) E. offline prize game / contest F. offline recreational activity (e.g. gymnastics session in the park, community walk)
6. Form of message / post In what format is the message conveyed?	A. text B. text & picture C. picture with inscription / title D. text & video E. video with inscription F. text with link G. link with inscription H. event
7. Interactivity	A. number of likes/dislikes B. number of comments C. number of shares D. number of markings E. number of questions