though they themselves have completed their school education. Non-use values often rely on deeply held historical, national, ethical, religious, and spiritual values. A different, non-utilitarian value paradigm holds that something can have intrinsic value; that is, it can be of value in and for itself, irrespective of its utility for someone else. For example, birds are valuable, regardless of what people think about them. The utilitarian and non-utilitarian value paradigms overlap and interact in many ways, but they use different metrics, with no common denominator, and cannot usually be aggregated, although both value paradigms are used in decision-making processes.

      How decisions are made will depend on the value systems endorsed in each society, the conceptual tools and methods at their disposal, and the information available. Making the appropriate choices requires, among other things, reliable information on current conditions and trends of ecosystems and on the economic, political, social, and cultural consequences of alternative courses of action. Assessments strive to be value free, using evidence-driven results. But in fact, all people involved in assessments come with value systems and need to explicitly state these values wherever they are at work. Another way to take advantage of different ways of thinking is to create diversity in the assessment in terms of background, region, gender, and experience in order to balance views.

Dealing with different knowledge systems

The IAASTD aims to incorporate both formal scientific information and traditional or local knowledge. Traditional societies have nurtured and refined systems of knowledge of direct value to those societies and their production systems, but also of considerable value to assessments undertaken at regional and global scales. To be credible and useful to decision makers, all sources of information, whether from scientific, local, or practitioner knowledge, must be critically assessed and validated as part of the assessment process through procedures relevant to the specific form of knowledge.

     Substantial knowledge concerning both AKST and policy interventions is held within the private (and public) sec-

tor by "practitioners" of AKST, yet only a small proportion of this information is ever published in scientific literature, and much is kept in less accessible gray literature. Again, broad participation can help include as many sources of knowledge as possible.

      Effective incorporation of different types of knowledge in an assessment can both improve the findings and help to increase their adoption by stakeholders if the latter believe that their information has contributed to those findings. At the same time, no matter what sources of knowledge are incorporated in an assessment, effective mechanisms must be established to judge whether the information provides a sound basis for decisions.

Modeling issues

Models are used in the IAASTD to analyze interactions between processes, fill data gaps, identify regions for data collection priority, or synthesize existing observations into appropriate indicators of ecosystem services. Models also provide the foundations for elaborating scenarios. As a result, models will play a synthesizing and integrative role in the IAASTD, complementing data collection and analytical efforts.

     It is relevant to note that all models have built-in uncertainties linked to inaccurate or missing input data, weaknesses in driving forces, uncertain parameter values, simplified model structure, and other intrinsic model properties. One way of dealing with this uncertainty in the IAASTD is to encourage the use of alternative models for computing the same ecosystem services and then compare the results of these models. Having at least two independent sets of calculations can add confidence to the robustness of model calculations, although it will not eliminate uncertainty.

     It should be stressed that the majority of "human system models" focus on economic efficiency and the economically optimal use of natural resources. Thus the broader issues of human well-being, including such factors as freedom of choice, security, equity and health, will require a generation of new models. To deal with these issues IAASTD must rely on qualitative analysis.