The history of evidence synthesis in health care
The search for clinical truth to support health care delivery has always been at the heart of enhancing outcomes for patients (Kereiakes & Antman, 2006). The apprenticeship model of learning that had been the source of almost all knowledge in previous centuries gave way to
an increasing information revolution (Laing, Hogg & Winkelman, 2004). There was an
explosion in medical textbooks at the turn of the century, which were then superseded by an increasing range of medical journals (Claridge, 2005). However, on its own, this
knowledge revolution could not deliver enhanced outcomes for patients (Forkner-Dunn, 2003), with research suggesting mild improvements in outcomes (Mckay, King, Eakin, Seeley & Glasgow, 2001). The most prominent concern raised by doctors at the outset of this revolution was the poor quality of much available information (Schactman, 2000). For many decades, there have been voices within health care raising alarm at the lack of evidence to support widespread clinical practice (Mulrow, 1987; Sackett & Rosenberg, 1995). This explosion in information in many ways compounded the problem and led to the development of a new movement to harness the great potential of such knowledge, Evidence-Based health care, first proposed in 1992 (Evidence-based medicine working group). One of the most widely accepted definitions of evidence-based health care was proposed by Sackett (1996: p71):-
‘The conscientious, explicit and judicious use of current best evidence in making decisions about the care of individual patients. The practice of evidence-based medicine means
integrating individual clinical expertise with the best available external clinical evidence from systematic research.’
Evidence-based health care involves the systematic collection, synthesis and application of all available scientific evidence, when available, not just the opinion of experts (Mohor, 1999). This represented a seismic shift from a position of expert based consensus guidance
Zaat, 2003. The most important element of the Evidence-Based health care movement is an acceptance of the evolving nature of clinical truth. Researchers have sought to quantify this, no more elegantly than Hall and Platell (1997). They demonstrated that the half-life of clinical truth in the surgical field is 45 years and therefore within half a century 50% of what is known is wrong. This more than anything cements the need for a contemporaneous and evidence based knowledge base, rather than an expert led knowledge base (Poynard et al., 2002).
As the field of evidence-based health care evolved, new organisations spearheaded the development of such techniques (Social Science Research Unit, 2009), as well as supporting the dissemination of the required methodologies (Oxman, 1994). A central part of these new methodologies was the use of meta-analysis – literally an analysis of analyses (Glass, 1976). Meta-analyses pool individual study data to provide an overall estimate of the effect under consideration, leading to a stronger conclusion than any of the individual studies (Abrams, Jones, Sheldon & Song, 2000).
The use of this technique has proliferated, particularly within evidence based medicine, because of its ability to estimate the effect of an intervention (Chan & Arvey, 2012). The strength of meta-analysis in this context was demonstrated in a key review describing the efficacy of corticosteroids given to pregnant women who deliver premature babies
(Crawley, 1990). The results of the meta-analysis of data demonstrated that administration of maternal corticosteroids significantly reduced morbidity and mortality among premature infants. The celebration of this discovery was tempered by the realisation that a similar meta-analysis of data up to a decade earlier in 1980 showed the same result. If the
techniques of evidence synthesis been applied, the outcomes for premature babies across the globe could have been impacted and much harm avoided (Woloshin, 2013).
So uneasy was the impact of this realisation, that it inspired the formation of one of the key entities in the globe in the field of evidence-based health care, the Cochrane Collaboration (2013). The Cochrane Collaboration is an international network of more than 28,000 dedicated people from over 100 countries. They work together to help healthcare practitioners, policy-makers, patients, their advocates and carers, make well-informed decisions about health care, by preparing, updating, and promoting the accessibility of
Cochrane Reviews (Tovey, 2010), published online in the Cochrane Database of Systematic Reviews, part of The Cochrane Library. So key was Crawley’s (1990) review to this
endeavour, the data was incorporated into their logo (Figure 4).
Figure 4. Meta-analysis from Crawley 1990 and corresponding data as part of the Cochrane logo
Cochrane led the formulation of the systematic approach to evidence synthesis, as categorised by systematic review (Doshi, Jones & Jefferson, 2012), to deal with the issues already highlighted by misuse of the tools of evidence-based health care (Mohar, 1999). Advocating the writing of a concise review protocol that is reviewed prior to work
commences and the use of clear criteria regarding inclusion and exclusion, quality, strength of conclusions and lay summaries. Cochrane reviews are viewed as the benchmark in supporting evidence based decision making (Olsen et al., 2001). Similar organisations developed symbiotically through the last 20 years, including the Campbell collaboration focussing on education and justice (2013), as well as EPPI centre in public health and education policy (2013)