In consultations many public health experts wanted to add a 'policy' class. There are several elements to be described. One element is the public health work of developing healthy public policy. Whether or not policy is implemented, substantial work goes into its development, and its availability can provide a head start for action on a health issue that becomes of interest. Information on existing public policy that has an impact on public health is considered by some as important to collect and integrateespecially in the absence of a national public health policy. Some public health experts were comfortable with the concept of 'policy' as a resource or as part of the public health infrastructure, however others were strongly negative -they saw that as putting policy too low in the class hierarchy. This reveals the tendency to see the toplevel classes listed in Figure 5 as a hierarchy of the factors of most importance to public health, in which case, where is policy? Where are population groups? The discussion in Section 3.2.3, which is illustrated in Figure 7 , addresses these questions.