Martín-Cantera et al. BMC Public Health 2010, 10:136 http://www.biomedcentral.com/1471-2458/10/136 Student’s t-test between continuous and categorical vari- ables. In order to analyse the association between the risk perception of an RTI (low/medium/high) and the different risk factors considered, an unconditional binary logistical regression model will be implemented. For the risk perception considered as an ordinal scale, a multiple lineal regression will be implemented. For the selection of the variables for the multivariate model, the metho- dology proposed by Hosmer-Memeshow [57], Cobo [58] and Greenland [59] will be implemented. In the initial multivariate model, the significant bivariate level vari- ables will be introduced, based on the level of signifi- cance p = 0.25 and the variables considered to be clinically relevant. Confusion, interaction and co-linear- ity factors will be analysed. The adjustment of the model will be evaluated using the Hosmer-Lemeshow test and the area under the curve. All statistical tests will be carried out with a confi- dence level of 95% and supposing a bilateral contrast. The analyses with be carried out using the statistics package SPSS. Quality control The variables collected during the interview with the health professional will be reviewed and checked against the patient’s clinical record during the same visit. Coor- dination meetings will be held with the collaborating researchers periodically. Any confusing or missing data will be revised by one of the investigators who will ask for explanations from the relevant investigator. Data col- lection booklets will be read using Teleform technology. The introduction of the data into the database as well as quality control will be carried out by a trained person with ample experience using Teleform. The interviewers carrying out the telephone interview will be trained and accredited periodically in order to ensure the maximum quality of data collection. Difficulties and limitations of the study In this study the relationship of risk factors of suffering an RTI will be evaluated; however, this does not apply to causality assessment, which would need a different specific study design. There may be subjects who, although are assigned to one of the participating centres, do not have an open clinical register there because it is the first time they have visited the clinic or because the record is on paper. In these cases, the clinical data will be collected during the inclusion visit. The computerised clinical registers (eCAP™ software or similar) may not be correctly updated in some cases, due to their recent addition to the clinic. The research- ers will complete the information in the inclusion visit and through the telephone interview. Page 6 of 9 There are some difficulties related to the measuring instrument (telephone interview and face to face inter- view), for ethical and legal reasons (consent form) as well as validity (there are no valid surveys designed to this effect). The researcher will carry out a pilot study to rate the difficulties in completing the survey. Only those health and medication problems more often found in our field will be analysed in this study. Alcohol intake and the consumption of psychoactive substances will be considered self reported. Biological tests will not be carried out because the objective is to obtain the data under the same conditions of actual clinical practice carried out in primary care visits. The generalisation of the results will be limited to an urban population. Ethical aspects The study will be carried out according to the principles contained in the Helsinki Declaration and its successive reviews and the Good Clinical Practice standards. The LESIONAT study protocol obtained approval from the corresponding Ethics Committee (CEIC IDIAP Jordi Gol). Consent form: the information will be provided verb- ally and in writing. The study subjects will have suffi- cient opportunity to ask about study details. Printing of the consent form will follow the rules contained in the Helsinki declaration as stipulated in article 12 under the first title of the Royal Decree 15/1999. Data confidentiality: in this study, only researchers and monitors/auditors will have access to the information on the participating subjects. Discussion There are various motives that justify the importance of this study. Primary health care is an advantageous loca- tion to carry out preventive interventions in RTI. In our country, according to data provided by the Primary Health Care Information System, 75% of the population consults a general practitioner at least in their life, and the average number of visits is between 5 and 6 yearly. Furthermore, public health cover in Spain is practically universal. This makes primary health care an ideal place for the study and implementation of preventive mea- sures in the RTI field. These could include warnings from the side effects of certain medication, the effects of psychoactive substances on driving skills to the impor- tance of the control and monitoring of chronic or acute illnesses that help the patient elaborate a real reception of their physical state and capacity to drive [60-62]. RTI pose health problems that are extremely high in magnitude and in social and health repercussions. The Catalan Public Health Plan contemplates this interven- tion as a priority objective, and so establishes the