Lines of defence for combined assurance models: a structured literature review

Abstract

This structured literature review (SLR) evaluates the current state of knowledge on Combined Assurance (CA) by examining and integrating findings from peer-reviewed academic journals. Its objectives are to identify topics covered in CA research, and conceptual inconsistencies or ambiguities, revealing gaps that could enhance understanding, and assessing the maturity level of CA. Topics that emerged were identification of core components of CA and the main stakeholders involved, classifications of the stakeholders within the lines of defence framework, incorporation of lines of defence into various CA models, tools used to strengthen CA, the level of CA adoption in organizations, and the advantages CA provides. The continued use of the outdated Three Lines of Defence (TLoD) model, mixed opinions on the updated Three Lines Model (TLM) of whether it is an improvement or regression, and contradicting evidence of its effectiveness in the banking sector create ambiguity and inconsistencies around CA. Slow adoption of TLM, lack of consensus on board roles as line of defence, and resistance to internal audit leading CA efforts add to ongoing uncertainties. Research gaps include limited exploration beyond TLoD/TLM, a focus mainly on South Africa, lack of study focused on failure of CA to detect corporate scandals timely, and insufficient evaluation of CA’s role in providing assurance on unethical leadership risks. Most studies focus on outward-facing aspects, such as assurance on integrated reporting (IR), while giving little attention to inward-facing or internal perspectives. Although publications are increasing, CA remains underdeveloped. The SLR provides a thorough overview, identifies key trends, highlights gaps, and suggests directions for future research on CA.