Study population, allocation and sample characteristics
The study population comprised journalists in the health field, broadly defined. Of the 100 journalists to whom paper questionnaires were sent, names and postal addresses of the first 62 on the convenience sample list were obtained from the World Health Organisation's list of members of the Health Communication Network by selecting all names where the person's title was listed as "reporter" or "journalist". The remaining 38 names and addresses were obtained from the membership lists of national organisations of health and science journalists.
The 100 names on the list were randomly allocated to a control group (n = 50) and an experimental group (n = 50) by using a computer script. Three questionnaires, two in the control group and one in the experimental group, were returned by the post office as non-deliverable, resulting in a control group of 48 and an experimental group of 49. Of the 97 questionnaires assumed delivered, 73 were to journalists in 20 Western and Eastern European countries, 21 to journalists in Canada and USA, and three to one journalist in each of the following countries: Japan, Israel, and Sri Lanka. All but eleven addresses appeared to be the recipients' workplace.
100 health journalists for whom we had no email address were sent a paper version of a questionnaire about barriers and facilitators to high quality health journalism. Five-hundred ninety four health journalists for whom we had email addresses had previously been invited to visit our website and respond to an Internet-based version of the same questionnaire .
All respondents received a cover letter inviting them to answer the questionnaire, and a non-stamped, pre-addressed, return envelope. Each respondent in the experimental group received two International Postage Vouchers – "Coupon-Réponse International", which could be exchanged at his or her local post office for stamps. Information on how to make use of the vouchers was included in the cover letter. Otherwise, the cover letters were identical. We reckoned that two vouchers would cover the cost of return postage from any of the countries to the study centre in Norway.
There was no follow-up of non-responders.