Schulz et al. BMC Public Health 2011, 11:108 http://www.biomedcentral.com/1471-2458/11/108 once. Every time the experimental groups visit the pro- gramme, ipsative feedback is given about their health behaviour. This implies that the health behaviour scores of the current visit are compared to the scores of the last visit; feedback is given about a potential change. Furthermore, all scores are saved and illustrated in a graph in order to give the respondent the option to monitor the total change process at a glance. Ipsative feedback is not available for the control group. Sequential Behaviour Tailoring (SeqBT) condition After receiving the health risk appraisal, individuals in the SeqBT condition are invited to choose one of the health behaviours for which they have received a red or orange traffic light. Respondents are encouraged to change the behaviour for which they are motivated most. After receiving additional questions regarding the various psychosocial constructs of the selected lifestyle behaviour, they receive personal advice on this beha- viour which aims at helping to change this health beha- viour during the first year of the study. At the follow-up measurements, individuals in this condition are asked to fill out a questionnaire about all behaviours. Again, they receive the health risk appraisal, including an overview consisting of five traffic lights. In cases where a respondent has successfully changed the selected behaviour, the option to choose a second beha- viour in the second year is provided. They are free to select one of the behaviours for which they receive a red or orange traffic light. In cases where respondents have not changed the first behaviour, they will be invited to change the behaviour for which they are motivated most in the second year. This may be the same behaviour as chosen in the first year, but the respondents may also select another lifestyle behaviour for which they have obtained a red or orange traffic light. Afterwards, they receive the questionnaire containing items about percep- tions (beliefs) regarding the behaviour they have selected to focus on as well as personal advice. If respondents fill in the test in the meantime, which means that they re-visit the programme without having received an invitation for a follow-up measurement, they only have to answer the questions concerning the selected behaviour in order to receive ipsative feedback on their chosen topic and personal advice if they are interested. Simultaneous Behaviour Tailoring (SimBT) condition Upon receiving the health risk appraisal, participants of the SimBT condition are not explicitly asked to select one behaviour which is in contrast to the SeqBT condi- tion. In cases where these participants do not adhere to the recommendation of one or more of the lifestyle behaviours, they obtain additional questions (psychoso- cial constructs) as well as personal advice on all Page 6 of 9 behaviours for which they receive a red or orange traffic light in the health risk appraisal. At every follow-up visit/re-visit, individuals are asked to fill out questions about all five lifestyle behaviours. In this way, the programme can check on which beha- viours the individual should receive personal advice con- cerning his or her perceptions. Moreover, they receive ipsative feedback concerning all five behaviours. Control condition During the first visit of the programme, respondents in the control condition receive the health risk appraisal. Afterwards, this group only receives e-mails requesting them to fill out questionnaires about the five lifestyle behaviours at follow-up at 12 months (T1) and 24 months (T2). The control group does not receive any personal advice throughout the term of this study. Primary and secondary outcomes Our first objective is to compare the effectiveness of the two different strategies for changing lifestyle with each other as well as with a control group. In addition to the effect studies, we will also gather and analyse data to realize additional outcomes: Process evaluation Process evaluations will be executed to assess levels of personalization and appreciation and to analyse which elements of the CT programme were most attractive and successful. We aim at gathering process evaluation data to analyse the factors facilitating and hindering the use of the web-based modules. All participants receive questions concerning the website (5 items; e.g., “In my opinion, the website is user-friendly"; totally agree - totally disagree), the health risk appraisal (12 items; e.g., “The health risk appraisal gives a good overview of my lifestyle"; totally agree - totally disagree) and two general questions (i.e., “Do you intend to re-visit the website in the future?"; yes, definitely - no, definitely not; “Do you have any general comments concerning the pro- gramme?"; open question). The two experimental groups additionally receive questions regarding the personal advice (15 items; e.g., “The pieces of advice are informa- tive"; totally agree - totally disagree). We will compare the evaluations of the three different groups to analyse differences with regard to the process evaluation data. Subgroup differences We aim at exploring potential differences between high SES and low SES groups, different age groups, men and women, and healthy and unhealthy people (defined by the items about health status). Power analysis The power analysis is based on detecting 10% differ- ences in behaviour between the different conditions.