The selected websites were chosen based on the results of a national survey that identified web-sources commonly used by Israeli school adolescents when seeking OHI . According to the survey, over 70% of students indicated having sought health information through Google.co.il, Finder, and Kafe. Five other search engines (Tapuz, Nana10, Walla, Bing, and Yahoo) were also mentioned in relation to searching for OHI, but less frequently. Therefore, several searches were conducted using identical search terms in Hebrew using Bing, Finder, Google, Kafe, Nana10, Walla, and Yahoo. Tapuz was excluded as it searches only within the Tapuz website itself.
Website quality evaluation
The quality of each website was assessed on three key parameters: accuracy/completeness, credibility, and usability.
Accuracy and completeness
Accuracy/completeness of the OC content was assessed based on 13 established content items selected by a family planning expert from contraception guidelines . Items that were misperceived by Israeli physicians in a study on OC misconceptions  (perhaps due to inconclusive scientific evidence) were excluded, as we were unable to definitively classify the information as accurate or inaccurate. The final list included items such as efficacy (e.g., of 1000 women using the pill as prescribed, 3 will become pregnant within a year), effectiveness in the first year of use (e.g., about 8% of typical users initiating OC will become pregnant in the first year of use), safety, reversibility, suggested frequency of use (e.g., pills should be taken daily), STI protection (e.g., pills do not protect against STIs), side effects (e.g., headaches, nausea, vomiting, breast pain/tenderness, weight gain, fatigue, mood changes), dose (e.g., take one pill a day until the pack is finished), back-up contraceptive method (e.g., use a backup contraceptive until taking 7 consecutive pills, if missing a pill, if late starting a new pack, or in case of severe vomiting or diarrhea), or instructions in case of missing a pill (e.g., taking another pill within 12 hours will still prevent pregnancy). The 13 items were assessed on a 4-point scale [inaccurate information (−1), information not presented (0), information partially presented (1), and information complete and accurate (2)], and computed on a composite percentage scale ranging from 0 to 100%, with a score of 26 (the maximum possible for this 13-item scale) representing 100%.
Basic aspects of the websites’ usability were also assessed by applying an 11-item instrument selected from the Minervation Validation instrument (questions 2.1.2-2.1.5, 2.2.1-2.2.3, and 2.3.4)  and/or the University of Michigan “website evaluation checklist” (questions 12, 28, 30, 34, and 35) . The items included aspects such as a “return to home page” option on all pages, consistency of functions and design, and appropriateness of content for the target adolescent audience (e.g., readability as assessed by amount and size of text, use of age-appropriate medical and scientific terminology). Each item was assessed on a 3-point scale [parameter absent (1), parameter partially addressed (2), and parameter fully addressed (3)], and computed on a composite percentage scale ranging from 0 to 100% with a score of 33 (maximum possible for the 11-item scale) representing 100%.
Classification of websites
The websites were classified as belonging to one of the following 5 categories: a) HMOs (i.e., websites of the four leading Kupat Holim), b) health portals (i.e., websites that provide information on a wide scope of health and medical subjects), c) contraception-specific (i.e., websites dedicated primarily to informing the public on the subject of contraception), d) promotional and commercial (i.e., websites whose goal is to promote a certain product, service, or brand), e) life style and women’s websites (i.e., websites that provide information on contraception in the context of women’s wellbeing and child-rearing advice).
All websites were evaluated by one of us (LF). Following analyses of the data and in response to a reviewer’s suggestion on a previous version of this report, six randomly selected websites (a total of 38 web pages) were independently assessed by YN and RS, and reassessed by LF. Some inter-rater variation was observed for accuracy/completeness and usability (Cronbach’s alpha coefficients–0.84 and 0.73, respectively; Additional file 1). A greater degree of variation was noted for the 15-item credibility scale, which revealed a Cronbach‘s alpha coefficient of 0.66. This value increased to 0.75 upon deletion of one item (“Is there a clear statement regarding the minimum age for the use or participation on the website?”). The credibility parameter for all 29 websites was therefore reanalyzed using the 14-item scale.
Mean scores, standard deviations (SD), ranges, and percentages were calculated for all websites and for category-specific websites. Pearson correlation coefficients of the three parameters assessed were estimated for all, and for category-specific websites.
Statistical analyses were performed using SPSS 17.0.