addition, there are so many estimates and assumptions in the data collection that, according to Nadev Malin (2002, p.10), unless the same researchers are studying the different products, it is nearly impossible to ensure that the inventories of inputs and outputs were compiled in a consistent manner. In the third or impact assessment (LCIA) stage, there is a particularly large measure of subjective involvement, both in the selection of the categories and in the weighting of categories according to their importance. Examples of impact categories are global warming, indoor air quality, acidification and toxicity (table 1). The categories employed by different national green building programs, for example, might feature attributes dictated by their ecological situation. Whereas Europeans might highlight a products contribution to acid rain, an Australian system might be more concerned with ozone depletion, and Africans more concerned with resource inputs (Berge, 2000). The impact categories selected may, however, simply have to do with the perspectives of the LCA designers. In the Australian LCAid system, for example, impact categories include carcinogenesis, heavy metals and pesticides, whereas the US BEES system uses the categories ecological toxicity, human toxicity and indoor air quality. Many of the programs for both products and for buildings allow program users to change the weightings in comparing materials for their specific projects. For example, the BEES program allows users (usually building designers) to adjust the ratio of environmental, health and financial factors.