Schulz et al. BMC Public Health 2011, 11:108 http://www.biomedcentral.com/1471-2458/11/108 actual performance of the behaviour. On the other hand, ability factors (i.e., action plans, goal action) can help to overcome these barriers. Intention is determined by the motivational factors attitude, social influence and self- efficacy, which in turn are influenced by awareness factors (i.e., knowledge, cues to action, risk perception), predisposing factors (i.e., behavioural, psychological, biological, social and cultural factors) and information factors (i.e., message, channel, source). The main goal of this study is to test and analyse the effects of two different strategies (i.e., sequential and simultaneous behaviour change feedback) using web- based computer tailored technology. The effects will be compared with those of a control group. Furthermore, we will conduct a programme evaluation and explore potential differences in effectiveness and appreciation of the intervention among subgroups (i.e., socioeconomic status- (SES), age- and gender differences) in order to optimize the programme so that it fits better to the indi- viduals’ characteristics, needs and preferences. Methods Design The current study is related to a larger study, which was approved by the Medical Ethics Committee of Maas- tricht University and the University Hospital Maastricht (NL27235.068.09/MEC 09-3-016). In that study, we assess level of adoption of the CT programme by focus- ing on three different exposure rates: first use of the intervention, prolonged use (staying on the intervention for a substantial period of time) and sustained use (revi- sits to the intervention). Besides this, satisfaction with the service will be carried out. The present study, which is registered at the Dutch Trial Register (NTR2168), consists of a randomized con- trolled trial (RCT) including two experimental groups, namely a Sequential Behaviour Tailoring (SeqBT) condi- tion and a Simultaneous Behaviour Tailoring (SimBT) condition, and a control group. The conditions will be described in detail below. A design with a baseline mea- surement and two follow-up measurements at 12 and 24 months is used. Participants, inclusion criteria and procedure The study is part of an initiative of different Dutch Regio- nal Health Authorities (RHAs) of the provinces North- Brabant and Zeeland. Our CT programme is partly inte- grated in the Adult Health Monitor 2009 which is con- ducted by the RHAs. With this monitoring instrument, the health status of people living in the Netherlands is assessed. Every four years, a representative sample of the population aged between 18 and 65 years is recruited in order to fill out this questionnaire. It contains the fol- lowing topics: demographics; aspects of general health Page 3 of 9 (e.g., physical health, mental health, social health, lifestyle behaviours); and health related topics (e.g., social and physical environment) [47]. As part of an additional ser- vice, participants completing this monitor online subse- quently obtain the opportunity to receive tailored feedback about their health behaviour via the new CT programme. Therefore, some data the person fills out during the Adult Health Monitor (e.g., demographics and data regarding the five lifestyle behaviours: smoking, alcohol intake, fruit consumption, vegetable consumption and physical activity) are copied to the CT programme. Before this, participants receive information about the purpose of the current study and an explanation of the use/handling of their data. We ask for written informed consent for their participation in the project. Confidenti- ality is ensured and it is explained to respondents that they could withdraw participation at any moment. Approximately three weeks after completing the moni- tor, participants who are interested in obtaining tailored feedback about their health behaviour receive an e-mail including an invitation to log in to the CT programme by use of their personal login code and password. After successfully logging in, respondents receive the health risk appraisal (i.e., feedback concerning their lifestyle and information about whether they meet the public health guidelines) based on their answers to the Adult Health Monitor, and the experimental groups receive some additional questions (i.e., attitude, social influence, preparatory action plans, self-efficacy, coping plans) and personal advice. The different parts of the programme will be described in detail below. The web-based CT programme To deliver personalized advice, three inter-related ele- ments are necessary: a screening instrument to measure demographics, health status, health behaviour and beha- vioural determinants; a message source file containing all tailoring messages; and a computer programme that offers the possibility to analyse the screening results and to select the correct messages from the message file [15,48]. The intervention programme is developed by means of the “TailorBuilder"-software (OverNite Software Europe B.V., The Netherlands). The TailorBuilder is a web- based instrument that was specifically developed to cre- ate and conduct online questionnaires and design and implement tailored advice. Respondents can login via a website on which general information about smoking, alcohol intake, fruit and vegetable consumption, and physical activity is given as well as detailed information about the study, frequently asked questions and a contact form. The web-based CT programme combines several pro- grammes which have already been proven to be effective in increasing smoking cessation [21], reducing the