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Table 3 Synthesis methods with appropriate sampling methods

From: Searching for qualitative research for inclusion in systematic reviews: a structured methodological review

Synthesis method Description Sampling method Rationale for sampling method
Critical interpretive synthesis A method of synthesis that offers a means of systematically producing explanatory theories directly from the data. (1) Purposive sampling;
(2) Theoretical sampling [65]
(1) Purposive sampling of representative cases used to immerse team in area of investigation.
(2) Followed up by pursuit of further lines of theoretical inquiry.
Grounded theory-based approaches An interpretive approach to synthesis that is modelled on the primary research methods of grounded theory. Theoretical sampling [34] Further lines of inquiry and hence routes for searching emerge from ongoing analysis of the data and hence require follow up along lines suggested by theory.
Meta-aggregation A structured, process-driven approach to systematic review of qualitative research modelled on the conventional systematic review of quantitative literature as practised by the Cochrane and Campbell Collaboration. Comprehensive sampling [49, 68] Seeks to identify all relevant studies in order to establish credibility in conventional systematic review terms.
Meta-ethnography An interpretive method for synthesising qualitative research of particular value in developing models that interpret findings across multiple studies. Purposive sampling [56, 57]
Theoretical sampling [34]
Interpretive focus places premium on identifying studies to contribute added value over and above current version of synthesis and thus requires sampling on a theoretical basis.
Meta-interpretation A meta-synthetic approach used specifically in interpretative synthesis. Maximal divergent sampling/maximum variation sampling [70, 72]; Theoretical sampling [70] Focus on interpretation requires that insights are maximised by exploring papers that are not characteristic of the “average sample.”
Meta-narrative synthesis Takes paradigmatic approach to map literatures from different research traditions. Purposive sampling of key papers [35, 62] Seeks an illuminative sample of papers from within different research traditions.
Qualitative meta-synthesis Attempts to integrate results from multiple different but inter-related qualitative studies with interpretive, rather than aggregating, intent, in contrast to meta-analysis of quantitative studies. Comprehensive (representative) sampling [55] Patterned on conventional systematic review methods therefore seeks all relevant studies to represent entire phenomenon of interest.
Realist synthesis Approach to complex social interventions or programmes which provides explanatory analysis aimed at discerning what works for whom, in what circumstances, in what respects and how. At different points uses variously:
(a) Comprehensive sampling [74];
(b) Purposive sampling [66];
(c) Theoretical sampling [34];
(d) Snowball sampling [61]
Comprehensive sampling (a) used to explore key focus of review. Becomes starting point for more explanatory exploration (b–d) of associated literature and mechanisms.
Scoping review Rapid review that aims to map existing literature in a field of interest in terms of volume, nature, and characteristics of primary research. Random sampling [74] Aims to characterise literature, not to document studies in minute detail, sampling representative body of literature may suffice for planning purposes.