Only a limited set of adaptation decisions can be formalised due to, among other factors, the intensive time, resource and capacity requirements of formal decision making methods. Further, for many decisions informal decision appraisal may be preferable. Research in psychology has demonstrated that informal methods have developed through evolutionary algorithms and can make them remarkably effective (Gigerenzer and Selten 2001). Indeed, there is good evidence that in the presence of limited or highly ambiguous evidence, and questionable information reliability, some evolved informal patterns consistently lead to better decisions than the attempt to apply more formal methods (Gigerenzer 2000).

For individual decision appraisal, there is a large literature within psychology and behavioural economics describing various informal decision making methods. Examples include methods for estimating and weighting probabilities (e.g. Tversky and Kahneman 1973; Kahneman and Tversky 1979; Weber and Hilton 1990), valuing the relative importance of outcomes (Fischhoff 1996; Viscusi, Magat, and Huber 1987; Samuelson and Zeckhauser 1988), and discounting future events (Laibson 1997; Karp 2003; Frederick, Loewenstein, and O'Donoghue 2002). When individual decisions are complex, and the costs of information gathering and processing become prohibitively high, it may be appropriate to make individual decisions informally on the basis of heuristics.

For collective decision appraisal, informal methods may be take a more deliberative form. For example, consensus-based decision making can facilitate discourse amongst a group to increase familiarity and shared understanding of the decision. This may increase a sense of shared control amongst different actors, and lead to more effective adaptation (Minkler and Wallerstein, 2011). There is an equally large range of methods, which address collaborative goal setting, which cannot be addressed by formal methods. These are described in Section 3.5.