Where Φ is the value of the function of a rule (0, 1), Γ is the standard value of the
coefficients that we have to esteem that include the coefficients β and α, X* is the matrix of
explicative variables where are present as the attributes of the urban transport as the
socioeconomic caracteristics of each individual.
3.- Analysis of the sample.
The estimation of the function of demand for transport by discrete choice model requires
knowing the individual behaviours in front of the choice of transport used, being posible, in
general, to apply well the declared preferencies or the revealed preferences (The MVA
Consultancy, 1994). In this essay real facts have been used, we start with a domiciliary
inquiry about movility in work days in the Bay of Cadiz, made by EPYPSA (1993) and
financed by MOTPMA and “Junta de Andalucia”. The number of inquiries made for the
area of study was 2.200 being distributed in a proportional way to a number of families in
each zone adapted previously in Rota, Puerto de Santa Maria, Cadiz, Puerto Real, San
Fernando and Chiclana. In Cadiz 786 inquiries were made and these families were asked
about the socioeconomic caracteristics and the urban travels made for every member older
than 5 years, being made with these facts three classifications, one about families, other
about people and the last one about urban travels.
The original sample consists on 5.565 observations that means the total of urban travels
made by the asked individuals in Cadiz. The first step consisted on determining the users of
urban and private transport in Cadiz, for this reason we chose all the urban travels that have
as origin and end the studied area, could be given the case of individuals that to travel to
other towns use in the first part of the way a car or the urban bus, and for this ought to be
included in the sample, however we verified that this situation was not usual. Then, we
proceeded to avoid in the sample the travels made on foot, that although are alot, they are
not an object of study, because we want to analyse only motorised travels; we avoided
travels made in laboral and scholar transport and by taxi too, for being non-representative
and being in need of the homogeneity needed to include them in some of the ways of study,
for this reason we only chose travels made in private car as driver or attendant and by bus.