The GPG concept is an extension of the economic tradition of classifying goods and services according to where they stand along two axes: one measuring rivalry in consumption; the other measuring excludability. Pure private goods are those that we are most used to dealing with in our day-to-day lives, and are defined as those goods (like a loaf of bread) that are diminished by use, and thus rival in consumption, and where individuals may be excluded from consuming them. At the opposite end of the spectrum are pure public goods, which are non-rival (not diminished by use) and non-excludable (if the good is produced, it is freely available to all). Public security is an often-cited example. In between these extremes are 'impure' goods, such as 'club goods', which have low rivalry but high excludability, and 'common pool goods', which have low excludability but high rivalry [2] . Clearly in this case, 'health' itself is a private good, as are the majority of goods and services used to produce health [3] .