OBJECTIVES: To review the existing literature on; i) the definition of the threshold ii) debate about its use, theory and value and, iii) robust theoretical methods for its calculation. METHODS: The traditional approach for literature searching makes use of key terms and Medical Subject Headings (MeSH) that most accurately capture the range of literature relevant to the piece of work while attempting to minimize irrelevant studies. This process requires a degree of expertise (and luck) as to the terms used, with the potential of missing related but differently specified areas of the literature and anything not captured in search engines.  The alternative approach is “pearl growing”. This approach uses a pool of relevant papers (“initial pearls”) to grow the literature both through references and citations until all relevant papers have been discovered. This approach therefore relies on the expertise of the authors of the published literature rather than the searcher’s knowledge of applicable terms. RESULTS: The traditional method of searching yielded 34 papers, only 17 of which were deemed relevant. In comparison pearl growing resulted in the identification of 76 relevant papers, including all of the 17 papers identified under the traditional strategy.  The focus of many of these papers was to debate the use of a threshold, the theory underlying it or its value.  A small number focused on methods for estimating its value, with a large majority using the social willingness-to-pay. CONCLUSIONS: The “pearl growing” approach offers a range of benefits over traditional methods, including the identification of papers and distinct sections of the literature not discovered otherwise, although it is limited by the existing software.  The cost-effectiveness threshold has been heavily debated, but there exists very little literature that attempts to provide a meaningful estimate of its value or even provide a theoretical framework for its calculation.