Services: these include key economic activities such as telecommunications, banking, insurance, land and water transport, aviation, accountancy, law, engineering, entertainment, etc., which can be produced in their own right or as a component of some product or another service. In Australia, using the method applied by the Australian Bureau of Statistics, services account for about 80% of employment and 75% of GDP. Other countries have different proportions, and some of the variations are due to different statistical methods rather than a basic difference in the way the economy works. The importance of services was not always recognized. Adam Smith's view was that "the labour of some of the most respectable orders in the society is, like that of menial servants, unproductive of any value, and does not fix or realize itself in any permanent subject, or vendible commodity, which endures after that labour is past, and for which an equal quantity of labour could afterwards be procured . . . In the same class must be ranked, some both of the gravest and most important, and some of the most frivolous professions: churchmen, lawyers, physicians, men of letters of all kinds, players, buffoons, musicians, opera-singers, opera-dancers, etc.". If this view of services was not consciously held by later generations, there was nevertheless frequently a tendency to underplay their role in the economy. There is no universally accepted definition of services. Several approaches have been tried, but none has received full approval. First, services are often characterized as intangible, invisible, incapable of storage and therefore requiring simultaneous production and consumption. These characteristics are already implicit in Adam Smith's remarks. Technological advances have, however, made this an obsolescent definition. Second, the institutional approach assumes that anything not classified as primary or secondary industry must be a service. Third, there is the functional approach, pioneered by T P Hill in 1977 when he defined services as "a change in the condition of a person or of a good belonging to some economic unit, which is brought about as the result of the activity of some other economic unit with the prior agreement of the former person or economic unit". Some have argued that this definition is deficient because it does not cover, for example, security services or preventive medicine. Fourth, the United States Office of Technology Assessment has proposed classification into two types: (a) knowledge-based services (insurance, professional and technical