Whilst working for the Bureau of Statistics of Papua and New Guinea in 1967, the author carried out a territory-wide population projection, based on a complete collection of village patrol reports and some birth records from a small sample of hospitals. Many years later, the author drew on this experience to develop a demolinguistic model for projecting the evolution of a bilingual community, which has been applied to nine language revitalization movements in Spain and in the British Isles. In the light of this, current literacy rates in Tok Pisin and in English in Papua New Guinea are discussed as well as the social conditioning of the spread of these languages.