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312 Institute of Certified Travel Agents
functions are linear in that any increase in demand
for the output of any sector will result in an
increase in demand for the factor inputs of that
sector in exactly the same proportion as those used
on average, to produce the current level of output.
Because input±output analysis attempts to
calculate the economic effects of changes in final
demand, it is intended to work on marginal
coefficients. However, the cost of deriving the
marginal coefficients of production functions is
such that the analyses tend to rely on average
coefficients. This means that some accuracy is
sacrificed in an attempt to keep the costs of
construction at a reasonable level. Studies that
have been undertaken in order to determine the
significance of this inaccuracy tend to suggest that
it is an acceptable level of inaccuracy, no more than
5 per cent in most instances.
Input±output analysis offers an extremely flexible
and robust framework for studying the
economic effects of changes within an economy.
If new sectors are introduced or existing ones are
removed then the framework is such that a revised
model would need to be constructed. However, this
shortcoming is to be found in any model that is
constructed to simulate the workings of the
economy. In order to construct a model that will
yield the level of detail found in input±output
models and to achieve similar or greater levels of
accuracy, it would be necessary to construct an
econometric model. This is a system of equations
whereby each of the equations reflect the production
and consumption functions of the economy.
These latter models are even more costly to
construct in terms of time and data, and their
results are less accessible to the planners and policy
makers who require the information.
Input±output analyses are not limited to calculating
economic impacts. They have been used for
a wide variety of purposes including travel models
and, more recently, environmental impact studies.
The advantage of using input±output analyses to
determine environmental impacts are enormous
because it means that the economic impacts
associated with a change in the level or pattern
of final demand associated with tourism spending
can be determined along with the environmental
effects of that change in activity. It also means that
the environmental impacts can be examined at the
direct, indirect and induced levels of impact in
much the same way as the economic impacts.
Further reading
Fletcher, J.E. �1989) `Input±output analysis and
tourism impact studies', Annals of Tourism Research
16: 514±29.
Leontief, W. �1966) Input±Output Economics, New
York: Oxford University Press.
O'Connor, E. and Henry, E.W. �1975) Input±Output
Analysis and its Applications, Griffin's Statistical
Monographs No. 36, London: Charles Griffin &
Co.
JOHN FLETCHER, UK
Institute of Certified Travel
Agents
The Institute of Certified Travel Agents �ICTA) is
an international non-profit organisation founded in
1964 to enhance the quality of professional tourism
practice through education, testing and certification.
Its pyramid of professionalism offers
education and recognition at every career stage.
For entry-level professionals, tests are given and
basic competency is stressed. This stage is followed
by the ICTA's professional certification process,
which offers two levels of recognition for experienced
professionals. One of these offers the highest
standards of professionalism and advanced knowledge
of business, industry, and global issues
necessary for expert practice in this field. In
addition to the educational activities, ICTA conducts
research in areas specific to its field of
operation. The headquarters of the institute is
located in Wellesley, MA, United States.
TURGUT VAR, USA
Instituto de Estudios TurõÂsticos
The Instituto de Estudios TurõÂsticos �IET) in Spain
was founded by a 1962 decree as Centralised
Public Service. Through its existence it has been
reorganised several times. Different general aims
have been entrusted to the IET, including market