The aim of the study is to assess the effectiveness of DMP compared to routine care in the primary care setting of two different German federal states (Rheinland-Pfalz and Sachsen-Anhalt). Since DMPs are liable to an implementation process ongoing at the moment which is differing considerably depending on several criteria (e.g. region of Germany, rural/urban area, health insurance) three groups will be observed: a "routine care group without DMP" (= control group; CG), a "DMP real group" (= DMP 1) and a group of patients participating in an (within the scope of the German law regulations) optimally in practices implemented DMP (= DMP 2).

The study is designed as a prospective cluster-randomized comparison of the two intervention groups (DMP 1 and DMP 2) against routine care as control group (Fig 1). The cluster randomization was chosen because this has optimal internal validity (absence of confounders) while avoiding contamination of interventions associated with patient randomisation.

• The German-Diabetes-DMP (DMP 1) is more effective than routine diabetes care (CG)

• An optimally implemented form of the Diabetes-DMP (DMP 2) is more effective than the German-Diabetes-DMP (DMP 1).

All data will be provided by the AOK. Data of the DMP groups are retrieved by the DMP documentation forms which have to be completed routinely every 3 to 6 months during the scheduled DMP visits of participating patients. The information about the tracer medication identifying patients of the control group is also provided by the AOK. The data reporting will follow the CONSORT recommendations for cluster randomized trials 16.

Data analysis will be performed according to the intention-to-treat (ITT) method. For missing data the 'last observation carried forward' -method will be used.

The minimum requirements for the Diabetes-DMP are regulated by law and defined in the RSAV 10. According to the legal regulations the intervention in the DMP1 group comprises consultations at 3- or 6-months intervals. During these consultations a detailed diabetes-specific anamnesis and physical examination incl. taking blood pressure and an analysis of HbA1c are carried out. Furthermore agreements are made concerning further treatment, e.g. target values for HbA1c and blood pressure and participation on patient education programs for diabetes or hypertension. All medical findings as well as the current medication have to be documented within structured, standardized documentation sheets at each consultation. If required a referral to a specialist (e.g. ophthalmologist) will be arranged. Furthermore the GPs get a special diabetes-handbook including current, evidence-based information about diabetes therapy. The GPs participating in the DMP1 group will receive no additional intervention.

There are major difficulties introducing new evidence into general practice requiring comprehensive implementation support at different levels (patients, doctors, practice team) 1718. Therefore, in the DMP 2 group implementation support at the level of doctors and practice team will be provided. In addition to the clinical interventions at patients level in the DMP group 1 several components aiming at optimizing the implementation process are provided in this group (= implementation interventions) (Table 2).

The control group represents routine care without DMP. There will be no intervention at all.

The study team will start to invite GPs at the end of September 2005. After receiving a written declaration of their willingness to participate in the study and to accept random assignment to the different groups GPs will be randomized.

Patient inclusion and pre-data collection will start in 2005. The observation period will be 24 months.

Since the interventions aim at the evidence based improvement of skills of GPs and practice teams serious risks or undesired effects for patients are not to be expected. There are no specific risks related to the study.

Previous to DMP participation patients already receive written and oral information about the content and extent of the DMP by their treating GPs, i.e. about potential benefits for their health and potential risks. Furthermore, patients are informed that DMP data including medical data will be analyzed. In case of acceptance they have to sign a special DMP participation form.

The study is being conducted in accordance with medical professional codex and the Helsinki Declaration as of 1996 as well as the German Federal Data Security Law (BDSG). DMP participation of patients is voluntary and can be cancelled at any time without provision of reasons and without negative consequences for their future medical care.

The study protocol was approved by the ethics committee of the University of Heidelberg in April 2005 (Approval-Nr. 098-2005). Furthermore the evaluation of the DMP is regulated by law in the Fifth Book of Social Code (§137 f. Abs. 4 SGB V).

The patient names and all other confidential information fall under medical confidentiality rules and are treated according to German Federal Data Security Law (BDSG).

Data management will be performed by the AQUA-Institute, Goettingen. All study related data are stored on a protected central server. Only direct members of the internal study team can access the respective files. Intermediate and final reports are stored at the office of the Department of General Practice and Health Services Research at the Heidelberg University Clinic.