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een the formalisation of the concepts of threshold
populations �the minimum number of people
needed to support a given industry), hinterlands
�the area containing the threshold population) and
hierarchies �the pattern of a few large cities offering
many goods and services and more offering fewer).
Models of tourism development from the perspective
of central place theory focus on the interaction
of destinations �as peripheral areas) and urban
markets �central places) such as Britton �1980).
Locational theory has developed a number of
concepts of general utility in tourism, four of them
listed here. First, location is important in determining
the success of a firm. Second, the choice of a
good location involves trade-offs among transportation
and production costs, resource and labour
availability, market accessibility and land costs.
Third, certain types of businesses do well if they
avoid locating close to competitors, others benefit
from such closeness, and still others are indifferent.
Finally, population size and the number and
location of competing firms limit the potential for
business growth.
References
Britton,S.G.�1980) Àconceptualmodeloftourismin
aperipheraleconomy',inD.G.Pearce�ed.),Tourism
in the South Pacific, Christchurch: Department of
Geography, University of Canterbury, 1±12.
Christaller, W. �1933) Die zentralen orte in Suddentdeutschland,
Jena: Gustav Fischer.
Miossec, J.M. �1977) `Un modele de l'espace
touristique', L'Espace Geographique 6�1): 41±8.
Von ThuÈnen, J.H. �1885) Der isolierte staat in beziehung
auf landwirtshaft und nationalokonomie, 3rd edn,
Berlin: Schumacher-Zarchlin.
longitudinal study
STEPHEN SMITH, CANADA
Longitudinal studies represent an examination of
phenomena over a period of time. Incorporating a
temporal element may involve retrospective study
�a time series of data which exists from the past to
the present) or prospective study �establishing a
system for data collection from the present into the
future). The value of this approach in tourism
research can range from increasing an understanding
of development processes in general, to
the changing experience of tourism for the
individual. The time scale employed could vary
from the length of a holiday to many years.
Longitudinal studies as a particular technique
stems from the growth of developmental psychology
in the late nineteenth century and its concern
with studying changes in behaviour over the
lifespan. In the 1930s, a series of longitudinal
studies were established to study child growth and
behaviour in the United States, some of which are
still being conducted. Problems common to most
longitudinal studies include the selection of appropriate
measures at the start of the study and the
maintenance of comparable data collection over a
time period. For instance, assessing the longer term
impacts of tourism on communities and environments
involves baseline data being gathered and
then systematically traced over time. Few tourism
projects include this form of research.
A technique related to longitudinal studies has
been the time series approach developed by
econometrics, where a set of data is ordered in
time with observations made at regular intervals in
order to isolate trends, cycles and periodic and
random events. Certain forms of statistical tourism
data are amenable to this type of approach and
have been used in economic studies of tourism �see
also statistics). Longitudinal and time series
approaches can also be related to wider concepts
of tourism development. The resort life cycle, for
instance, depends for its validity on adequate,
comparable data which is available over a
considerable period of time. Longitudinal studies
of tourism can also, in theory, be applied at the
individual level. The changing role of tourism
within a person's life cycle �from youth to old age)
has been little researched. This approach would
require a long-term, prospective research methodology,
which has been used in health studies and
could be applied to the field of tourism.
See also: change; economics; impact
Further reading
longitudinal study 363
Pearce, D. �1989) Tourist Development, 2nd edn,