[Health information on the Internet and trust marks as quality indicators: vaccines case study].

OBJECTIVES: To find out the prevalence of quality trust marks present in websites and to analyse the quality of these websites displaying trust marks compared with those that do not display them, in order to put forward these trust marks as a quality indicator.

DESIGN: Cross-sectional study.

SETTING: Internet.

PARTICIPANTS: Websites on vaccines.

MAIN MEASURES: Using "vacunas OR vaccines" as key words, the features of 40 web pages were analysed. These web pages were selected from the page results of two search engines, Google and Yahoo!

RESULTS: Based on a total of 9 criteria, the average score of criteria fulfilled was 7 (95% CI 3.96-10.04) points for the web pages offered by Yahoo! and 7.3 (95% CI 3.86-10.74) offered by Google. Amongst web pages offered by Yahoo!, there were three with clearly inaccurate information, while there were four in the pages offered by Google. Trust marks were displayed in 20% and 30% medical web pages, respectively, and their presence reached statistical significance (P=0.033) when fulfilling the quality criteria compared with web pages where trust marks were not displayed.

CONCLUSIONS: A wide variety of web pages was obtained by search engines and a large number of them with useless information. Although the websites analysed had a good quality, between 15% and 20% showed inaccurate information. Websites where trust marks were displayed had more quality than those that did not display one and none of them were included amongst those where inaccurate information was found.