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The Delphi technique is a research methodology which has traditionally been used to gain consensus among experts on complex issues characterised by uncertainty. Pioneered by the Rand Corporation in the 1950s for military applications, it has since been widely adopted across various fields, including nursing, health and social sciences and information systems on an array of multifaceted real-world issues. However, since its inception, the Delphi technique has undergone substantial methodological development and its use has now gone beyond its initial rationale. In the last two decades there has been a growing body of work illustrating an increasing methodological diversity of the method. While such diversity presents possibilities, it also challenges traditional application and methodological rigour. In an attempt to preserve the integrity of the method, generic and discipline specific guidelines have emerged providing general principles and standards. The aim of this paper is to present a much-needed critical reflection on the current application of the Delphi technique and its methodological development and to build on our paper from 2001 (Keeney et al., 2001). While the development of the Delphi method and its evolution are well recognised and reported in the literature, some controversies surrounding the approach remain and it is timely to revisit the method with a critical eye. Ultimately, the Delphi technique's flexibility is its significant strength, enabling the exploration of novel lines of inquiry, but it also presents a challenge. Striking the right balance between flexibility and rigour can lead to more meaningful insights and actionable outcomes from a Delphi study. Yet to achieve this, some level of consensus may need to be reached on the Delphi technique itself. In recognition of its 60th birthday, it is an opportune time to re-examine its key aspects and methodological advances and reflect on 'when is a Delphi not a Delphi?'
Hasson et al. (Mon,) studied this question.