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Correspondence (letter to the editor): Sponsor bias.

Disease management programs (DMPs) are complex interventions, and, like all medical interventions, they should undergo adequate scientific evaluation before being widely implemented into healthcare services, in order to find out their positive and negative effects and bear these in mind when treating patients. As the patients who are accepted into a DMP differ from those who cannot participate in these programs for whatever reason owing to legal regulations alone, a reliable evaluation of the DMP effects can be done only by means of a prospective randomized controlled trial (RCT). Unfortunately, and in spite of existing concepts and study protocols, it was not possible for those responsible to shape the introduction of DMPs in 2002 in such a way that they were accompanied by such a valid evaluation. Linder et al attempt to use the methodological concept of the propensity score approach in order to describe the effects of the T2DM (1). In this, they were unsuccessful because the comparison parameters are not fairly distributed between the intervention group and the control group. The method of retrospective control group formation is subject to the so called sponsor bias, in which the results of a study are distorted, consciously or unconsciously, into the direction desired by the sponsor (2). Since a prospective evaluation of DMPs in the setting of an RCT is unlikely, future evaluations of DMPs will also have to apply methods that are prone to distortion. In order to minimize “sponsor bias,” such evaluations should be organized jointly by health insurers that are interested in a “positive” result and health insurers that are interested in a “negative result” and conducted by an independent body.