Schulz et al. BMC Public Health 2011, 11:108 http://www.biomedcentral.com/1471-2458/11/108 consumption of alcohol [19], promoting the intake of fruit and vegetables [25], and increasing the level of phy- sical activity [28]. Tailoring algorithms that combine the responses of a person on specific questions with concur- rent feedback messages generate highly personalized advice to the respondent which they receive on their screen and that can also be printed. The following two paragraphs describe the questionnaire and the advice components in more detail. Measurement instruments Demographic information The following demographic variables are measured: age, gender, height, weight, marital status, religious back- ground, ethnicity, educational level, current work status, and income. Health status Respondents are asked if they suffer from high blood pressure and different kinds of diseases, such as diabetes and cancer. To measure quality of life, the SF-12 Health Survey [49,50] and the Mental Health Inventory (MHI- 5) [51] are used. To assess symptoms of depression and anxiety, the Kessler Psychological Distress Scale (K10) [52] is used. Lifestyle behaviours Smoking is measured by the abbreviated version of the Fagerström Test for Nicotine Dependence [53]. Alcohol consumption is measured by the Dutch Quantity-Fre- quency-Variability (QFV) questionnaire [54]. Fruit and vegetable intake is measured using Food Frequency Questionnaires (FFQ) for fruit and vegetable intake [55]. Physical activity is measured by the Short QUestion- naire to ASsess Health-enhancing physical activity (SQUASH) [56]. Intention The intention to change behaviour is measured by one item. This item is an extended version of the ‘stages of change’ concept [46,57] using an algorithm consisting of ten stages varying from unawareness to maintenance. Attitude To measure attitude concerning the different health behaviours, participants have to indicate on a five-point scale to what extent they ‘totally disagree’ or ‘totally agree’ with a total of six statements. Pros (i.e., advan- tages) of the health behaviour under consideration are assessed by three items, such as “Regular physical activ- ity is good for my health”. Cons (i.e., disadvantages) are assessed by another three items, such as “Regular physi- cal activity costs a lot of time”. Social influence Social influence is measured by three different concepts, namely social norms, social modelling and social sup- port. Social norms are assessed by one statement regard- ing the opinion of the direct environment (i.e., partner, Page 4 of 9 family members, friends and colleagues) concerning each health behaviour. Respondents are asked to com- plete statements, such as “According to the people within my direct environment...”, by choosing one of five options ranging from “I certainly should not smoke” to “I certainly should smoke”. Social modelling is assessed by asking the participants how many people of their direct environment engage in the healthy beha- viour, e.g., eating at least two pieces of fruit every day. A five-point scale is used, ranging from ‘everybody’ to ‘nobody’. Social support is measured by one item asses- sing the degree of support respondents receive from their direct environment to engage in the healthy beha- viour, on a four-point scale, ranging from ‘yes, they sup- port/stimulate me a lot’ to ‘no, they do not support/ stimulate me at all’. Preparatory plans Preparatory plans are measured by three items for each health behaviour, such as “I intend to become a member of a sports club”. Respondents have to specify whether they have the intention to use a specific preparatory plan in order to adopt the particular healthy lifestyle. A five-point scale is used, ranging from ‘yes, definitely’ to ‘no, definitely not’. Self-efficacy Self-efficacy is measured by means of six items. Partici- pants have to indicate on a five-point scale to what extent they feel able/unable to engage in or refrain from the key health behaviour when encountering difficult situations (i.e., situations that might lead to the perfor- mance of the unhealthy behaviour), e.g., “I am able to drink not more than two glasses of alcohol when I am at a party”. Coping plans Coping plans are assessed by asking participants to indi- cate on a five-point scale to what extent they agree/dis- agree with a total of six statements. Every statement deals with a specific plan regarding how to cope with difficult situations, e.g., “I have made a plan to be suffi- ciently physically active even when I have a great deal to do”. These questions are based on the difficult situations used for the self-efficacy items. Feedback procedure The message source file generates the tailored pieces of advice about the health behaviours, attitude, social influ- ence, preparatory plans, self-efficacy and coping plans. Hence, respondents receive tailored pieces of advice on their computer screen immediately after completion of each part (concept) of the questionnaire in order to avoid a very long text at the end of the programme. Either text-based messages or graphic feedback are given, in addition to pictures. Besides, in some pieces of advice, links to detailed information are added for