[Quality appraisal in systematic reviews of normative literature. A problem analysis]

Systematic reviews aim at searching, selecting, analyzing and synthesizing scientific literature in a transparent and systematic way in order to inform decision-making in the health care system on the basis of the best available evidence. In recent years, such reviews have also gained importance also in bio-, public health- and research ethics, as well as in health technology assessment. Such reviews do not only analyze ethically relevant empirical literature (e.g. on risk and benefit), but normative literature as well, i.e. literature consisting of ethical arguments. As the appraisal of the literature that should be included is paramount for a systematic review, the problem of how to appraise the quality of normative literature arises. This problem has not yet been solved satisfactorily. After developing a pragmatic definition for "normative literature", a typology of different types of systematic reviews of normative literature is presented. Based on existing approaches for quality appraisal, this paper identifies three possible strategies for solving the problem of quality appraisal of normative literature, and discusses their respective strength and weaknesses relative to the different types of systematic reviews. It becomes apparent that none of the existing approaches is able to solve the problem of quality appraisal in a general and convincing way. The paper concludes with stating minimal conditions regarding the elaboration of future strategies, and outlines a promising strategy that is theoretically acceptable and practically feasible.