BMC Public Health 2009, 9:100 http://www.biomedcentral.com/1471-2458/9/100 Internet. A fourth self-testing option is that of so-called street-corner tests, i.e. tests offered by organizations to consumers in public places like supermarkets. In a street- corner test, a sample is taken by trained personnel, and results are made available immediately. All these tests are offered directly to consumers without the need for a doc- tor's recommendation. In the true self-test situation at home, the consumer is responsible for all aspects of the tests: execution, interpretation and follow-up behaviour. Self-testing seems to fit in with current views about con- sumer autonomy and self-management, and may empower consumers to assume control over their own health care. Self-tests can offer privacy, convenience and reassurance to consumers, as well as earlier diagnosis and treatment. On the other hand, self-tests can cause distress when they yield false-positive results. They can also cause delay of treatment in the case of false-negative results, as well as in the case of true-negative results, when certain symptoms are actually due to another condition [2-6]. Dutch media have reported that the use of self-tests is increasing, but the extent of their use in the Netherlands has hardly been studied. Self-tests are likely to become more easily available and more widely used as the propor- tion of people having access to the Internet continues to increase [7]. Self-testing, and especially an increase in self- testing, may have important implications for the use of health care services by self-testers and for consumer edu- cation about the use and value of self-tests. The first prior- ity, however, is to gain information about the extent of self-test use. The aim of the present study was therefore to investigate the prevalence of the use of self-tests, as well as the type of tests that are most frequently used, and the association between demographic factors, health-related lifestyle fac- tors, health status and self-test use. Only those self-tests were studied that involve in-vitro tests on body materials, and that are initiated by consumers with the aim of diag- nosing a particular disorder or condition. Pregnancy tests were excluded from this survey. Methods Study population and procedure Participants were recruited from an existing Internet panel that is managed by Flycatcher, an institute for online research associated with Maastricht University. Anyone who is aged 12 years or over and has an e-mail address can apply to join the panel via the Flycatcher website http:// www.flycatcher.nl. Recruitment of panel members takes place through various channels: 'send-to-a-friend' cam- paigns among existing panel members, newsletters, data- bases with addresses kept by third parties (after permission), other private panels (after permission), and mouth-to-mouth advertising. If certain subgroups are underrepresented, special campaigns are organized, such as a 'send-to-a-friend' campaign aimed at the specific sub- group. Panel members are invited to participate in a study by being sent an e-mail explaining what respondents are expected to do, what the topic of the questionnaire is, and how much time it will take to fill in the questionnaire. An incentive for participation is offered in the form of a gift voucher that panel members can earn by responding to several questionnaires. The Flycatcher institute offers the opportunity to draw a sample from the entire panel, which is representative of the Dutch population. To this end, important background variables of panel members (e.g., age, sex, education, postal code, nationality and country of origin) are com- pared with the latest data from Statistics Netherlands. Compared with the Dutch population, the entire panel is younger, includes more women and is more highly edu- cated [8]. Since the extent of self-test use was unknown, we decided to use the entire panel to ensure that we would discover a reasonable number of self-testers. In September 2006, a short questionnaire in Dutch was thus sent to 12,529 per- sons aged 12 and over. Self-tests were defined in the intro- duction to the questionnaire, which specifically mentioned that pregnancy tests and monitoring tests were excluded from the survey. The questionnaire remained online for 8 days. A reminder was sent to non-responders after 5 days. Ethical approval for the study was obtained from the Medical Ethical Commission of Maastricht Uni- versity/Hospital. Questionnaire A literature review we had performed in preparation to the study revealed a lack of published research on self-tests and the frequency of their use and associated factors, and consequently also on questionnaires about self-testing. We therefore assessed self-test use and possible associated factors with a newly developed short questionnaire. We first conducted an Internet search to identify self-tests that were potentially available to the general public in the Netherlands in 2006, and found self-tests for over 25 con- ditions, which came in four different types (see Back- ground section). The conditions included in the questionnaire were based on consensus among the research team and external experts. In addition to data about previous and potential future use of self-tests, the questionnaire collected data about demographic and soci- odemographic factors, health status and health-related lifestyle factors. The selection of these variables was based on the assumption that they might be associated with self- test use, as previous research had shown that these factors are often related to health-related behaviours in general. Page 2 of 6 (page number not for citation purposes)