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154 disease
dependent variable), and to predict the likelihood
that an observation will belong to a particular
group. Discriminant analysis can be used to
investigate differences in tourism patterns �the
independent variable) among groups as defined
by trip purpose �for example, business versus
pleasure) or seasonality �the dependent variable).
Its predictive function might be used to classify
potential customers to differing marketing programmes
depending upon known social, economic
and geographic characteristics.
Discriminant analysis involves deriving a linear
combination of the independent variables that
maximise the differences among groups. Two key
assumptions that underlie the estimation process
are multivariate normality of the independent
variables and equal variance among independent
variables for each group defined by the dependent
variable. Parameter estimates are very sensitive to
multicolinearity among the independent variables
�this is the degree to which two independent
variables are correlated), sample size and the share
of observations among groups. It is generally
recommended that a ratio of twenty observations
is needed for each predictor variable and that each
group �depending upon number) includes at least
10 per cent of all observations.
Application of discriminant analysis usually
follows a three-step process: estimation, validation
and interpretation. The researcher should use
theory combined with the specific goal�s) of the
study as the basis for selecting the dependent and
independent variables. The validation process
includes testing for the generalisability of the results
and the classification accuracy of the model.
Interpretation is accomplished by identifying significant
independent variables, ordering them by
degree of influence regardless of sign, calculating
gaps between group means for each significant
variable and then assessing these results within the
context of the theory which underlies the study.
See also: classification; cluster analysis;
marketing research
Further reading
Morrison, D. �1976) Multivariate Statistical Methods,
New York: McGraw-Hill. �Provides a foundation
for application of this technique in tourism
research.)
Zimmer, Z., Brayley, R. and Searle M. �1995)
`Whether to go and where to go: identification of
important influences on seniors decisions to
travel', Journal of Travel Research 33�3): 3±10.
�Discusses an example of discriminant analysis in
assessing the factors affecting travel choices.)
disease
DANIEL R. FESENMAIER, USA
JIANN-MIN JENG, USA
Disease conveys lack of health in body or mind.
From ancient times, it has been both a reason for
and consequence of travel. The need for health
advice, preventive measures and treatment have
led to the establishment of medical specialism,
tropical and travel medicine, and even special
clinics. Diseases typically acquired when travelling
include bowel infections, sexually transmitted
diseases such as AIDS and vector-borne illnesses
like malaria.
PETER GRABOWSKI, UK
disembarkation card see arrival/departure
card
displacement
Displacement is a process resulting in something
being replaced. One group of tourists may
replace another or some of their activities may
just be replaced. Local people, built or natural
resources �such as wildlife) may be replaced or
values/habits altered. Displacement may be confused
with substitution, and signals lack of
socially or ecologically sustainable tourism
development.
JAY BEAMAN, CANADA