Organisational matters Figure 2 Calculating safety credits. Two separate clinical organisations institute different harm-reduction projects, aimed at reducing locally relevant causes of regulated preventable adverse event (PAE) classes. Project impacts in reducing the incidence of PAEs are audited, and then a weighting index converts PAE reductions into a common costable metric, such as days in length of stay prevented. The aggregate cost of all projects for an organisation, expressed as the total number of harm reduction units (HRUs) achieved, is then compared with the organisation’s target HRUs. Surplus HRUs generate tradable credits, to be bought by organisations that miss targets. There is also significant opportunity for new players to enter the market. Businesses may emerge to exploit ways of minimising PAEs. A manufacturer of computer prescribing systems could audit their impact on medication errors, and the number of safety credits generated if a system were installed. Remotely monitoring the health status of older people at home could demonstrate a reduction in falls due to early intervention generating safety credits. Entrepreneurs could pay consumers to wear medication allergy armbands by demonstrating the bands reduce PAEs due to inappropriate medication. Brokers could help organisations find credits, agree a price, arrange their purchase and meet regulatory requirements. Aggregators could help smaller organisations with similar safety profiles to work together, sharing experiences, minimising resource utilisation on harm reduction projects and maximising their ability to generate credits. To develop and test this new approach, we must understand the impact of the different possible market settings and ensure that benefits of error reduction strategies outweigh costs. We need to recognise that there is not a single market design but that a broad spectrum of design and implementation options are available, ranging from lighter weight models through to large, expensive and potentially heavily bureaucratic implementa- tions. The evidence for the most effective market settings and designs will come from a number of sources. First, we need to learn from existing MBC approaches such as carbon trading. Careful consideration needs to be given to current experience with baseline-setting mechanisms, the regulator’s role, auditing and verification procedures so that consensus can be reached on these issues by the healthcare community, as well as on the structure of the marketplace itself (will it be a registry, a 102 clearing house or a trading floor?). The market should ensure that large organisations do not distort credit prices. Some strategies will require early retirement of capital stock and generate short-term losses, or acquiring expensive new systems like electronic health records, while benefits are longer term. Exploring the costs and benefits of different points in this large space of policy and implementation options is unlikely to be feasible through large-scale trials alone. In silico computer simulations offer a powerful alternate experimental model, which can help test out these many different market variations quickly and cheaply.19 Once there is sufficient evidence from simulations and other analyses that a particular MBC model shows promise in principle, the next step will undoubtedly require one or more small pilot studies. Pilot studies would be followed by larger-scale trials, for example using cluster randomisation, at a regional level among hospitals, to ensure that we are making evidence-based policy about harm reduction. OVERCOMING OBJECTIONS We anticipate objections. Should we leave something as important as safety to a market, when governments have so clear a responsibility? Is it right to treat safety as a tradable commodity? One response is that health systems have tried many other strategies, but the patient safety problem seems entrenched and policy-resistant.20 The point is not whether commoditisation of safety leaves us feeling uncomfortable but whether it works. Others may point to criticisms of Kyoto that suggest better abatement can be achieved through taxes, or new technologies, and that too is a debate worth having. Another major source of objection is the potential for MBC to introduce complex measurement, verification and trading systems, with significant compliance costs and with the risk of building a bureaucracy that is expensive, and could become disconnected from, and in conflict with, the clinical services it is meant to be helping. With much evidence now pointing to the need for clinicians to be actively engaged in quality improve- ment for it to be successful, the design of any MBC administrative structure needs to ensure it is well suited to the culture and nature of clinical services. However, it is also worth reminding ourselves of the current state of affairs. It has been estimated in the USA that adults receive recommended care just over half the time (55%)21 and for children, just under half the time (46%).22 Composite indicators for safety and quality that track improvement over time show that the rate of response to current safety and quality programmes is unac- ceptably slow.23 Clearly, poor quality and unsafe care remains a profound cost to the health system. As long as the benefits significantly outweigh costs, we believe that the size of any MBC system should not of itself be an issue. So, in short, market forces, aphoristically labelled ‘‘the invisible hand’’ by Adam Smith, can be extremely efficient and powerful drivers of change. MBC may be the key to effective healthcare reform, promoting safety and error reduc- tion, and may become a widely used governance mechanism, directed at many aspects of healthcare service delivery. Funding: This research is supported by a grant from the Australian Research Council (LP0775532), and NHMRC Program Grant 568612. Competing interests: None. EC declares that he originated the safety market concept, participated in the developing the concept and the writing of the paper. JB declares that he participated in developing the safety market concept and the writing of the paper. Qual Saf Health Care 2009;18:99–103. doi:10.1136/qshc.2007.025833