Decisions about lumping vs. splitting of the scope of systematic reviews of complex interventions are not well justified: a case study in systematic reviews of health care professional reminders

Objectives: Lumping and splitting refer to the scope of a systematic review question, where lumped reviews are broad and split are narrow. The objective was to determine the frequency of lumping and splitting in systematic reviews of reminder interventions, assess how review authors justified their decisions about the scope of their reviews, and explore how review authors cited other systematic reviews in the field.

Study design and setting: A descriptive approach involving a content analysis and citation bibliometric study of an overview of 31 systematic reviews of reminder interventions.

Results: Twenty-four of 31 reminder reviews were split, most frequently across one category (population, intervention, study design, outcome). Review authors poorly justified their decisions about the scope of their reviews and tended not to cite other similar reviews.

Conclusion: This study demonstrates that for systematic reviews of reminder interventions, splitting is more common than lumping, with most reviews split by condition or targeted behavior. Review authors poorly justify the need for their review and do not cite relevant literature to put their reviews in the context of the available evidence. These factors may have contributed to a proliferation of systematic reviews of reminders and an overall disorganization of the literature.