26 Accounting for Health Impacts of Climate Change variable. For any given draw of specific values, the net present value of the adaptation option is calculated. This computerized process is then repeated a large number (many thousands) of times. The outcome of the analysis is a probability distribution of net present values. This probability distribution allows the computation of an “expected” net present value of the adaptation option under consideration instead of solely a given net present value, or a range of net present values. The same probability distribution also allows one to estimate the probability that the net present value of the adaptation option be negative. The conduct of probabilistic analysis is demanding if performed manually. However, packaged software allows the conduct of Monte Carlo simulation analysis in a relatively simple way. It is important to note that the conduct of risk (or probabilistic) cost–benefit analysis is an important recommendation already applied by ADB since 2002 to supplement the simplistic use of sensitivity analysis. Decision Rule It should not be presumed that adaptation (climate proofing) should be pursued wherever technically feasible. From an economic point of view, climate proofing may not be the best course of action in a number of specific circumstances. The outcome of the economic analysis of adaptation options, summarized as the net present value of these options, will guide the nature of the recommendations. The decision rule guiding the selection of adaptations is similar to the decision rule for any investment project: If only one technically feasible adaptation option exists, then the decision rule is: If Expected Net Present Value > 0 Recommend implementing the adaptation option If Expected Net Present Value < 0 Recommend rejecting the adaptation option (do nothing) If more than one technically feasible adaptation option exists, then the decision rule is to select the adaptation option with the largest expected net present value. If all adaptation options were to yield a negative expected net present value, then the best option is to do nothing. Prioritize and Select Adaptation Option(s) In circumstances when more than one adaptation option is technically feasible, the analysis should result in a prioritized list of adaptation options for implementation, which are selected from among several possibilities. Their prioritization can be based on an assessment of their technical feasibility, as well as their benefits and costs, social acceptability, and the opportunities they may offer for synergies with national priorities. While the use and outcome of a cost–benefit analysis may be given more weight in the prioritization process, it is important to recognize that other factors and criteria’s may also influence decision making. The challenging aspects of adaptation planning are the requirement of multidisciplinary skills and competencies. Options must be scientifically sound, socially beneficial, and economically viable. Roundtable discussions involve project engineers, environmental specialists, social safeguards experts, health experts, nongovernment organizations, implementing entities, and national climate change representatives. This is discussed in further details in the next section. A Collaborative Approach Confalonieri et al. (2007) suggest the following major challenges for research on climate change and health must be addressed: (i) development of methods to quantify impacts of climate and weather on a range of health outcomes, particularly in low- and middle-income countries; (ii) development of healthimpact models for projecting climate change–related impacts under different climate and socioeconomic