Using scoping reviews as precursors to systematic reviews: a typology and practical guidance derived from eight worked examples.

OBJECTIVE: Scoping reviews are often conducted as a precursor to a systematic review, yet guidance on how this relationship should be planned, executed and reported is limited. We aimed to illustrate, through worked examples, the ways in which scoping reviews can function as precursors to systematic reviews and to derive practical guidance for teams planning linked or sequential syntheses. STUDY DESIGN AND SETTING: We undertook a methodological analysis of eight contemporary evidence-synthesis papers and protocols spanning veterinary medicine, animal welfare, public health, mental health, occupational health and patient-and-public involvement, identified through the authors' knowledge of the evidence-synthesis literature. Each paired a scoping review with a systematic review. For every example we charted the structural relationship between the two reviews and the specific functions performed by the scoping stage. RESULTS: Across the eight purposively selected examples, four structural configurations were identified: (i) integrated sequential designs reported within a single project or paper; (ii) an antecedent, separately published scoping review whose search and records are inherited and extended by a later systematic review; (iii) a single "parent" scoping review that seeds several targeted systematic reviews; and (iv) a complementary scoping review run alongside a systematic review to contextualise sparse evidence. Across configurations, scoping reviews delivered seven recurring functions: feasibility and volume assessment; prioritisation of a tractable question; concept and definition clarification; eligibility and appraisal-tool decisions; search architecture and a reusable record set; gap identification; and conceptual or logic frameworks to structure synthesis. CONCLUSION: Scoping reviews can provide important foundational work for systematic reviews. Drawing on these illustrative examples, we propose a decision framework and reporting recommendations to help teams refine the specific purpose of a scoping review used as a precursor.