16
Each site visit has both a money price (p4) and a time price (t4). The money travel
costs include round trip vehicle cost per mile, plus other travel expenses. On-site time is
considered largely exogenous because most of the whalewatching at two of the three
sites, Monterey and Half Moon Bay, occurs on boat trips of fixed length. Variations in
onsite time are relatively small at the third site, Point Reyes, and in all cases
whalewatching was a day trip activity. Household income before taxes was the money
budget variable, and the respondent's time spent not working is the leisure time budget;
this is obtained from the average hours worked per week and the number of days of paid
vacation per year. The money and time budget levels for each individual were used as
the deflators, so normalized money price of site j is p48 œ p4/M, normalized time price of
site j is t48 œ t4/T, normalized money and time prices are M8œ1 œT8, full prices are
p0 = P. 38 ’ t8, and full budget is M0 = 1 + 38, with 38 estimated as a constant. The
quality variable, z4, is the number of whales vistors to each site expect to see. Table 2
Provides a summary descriPtion of these variables for each of the three sites.
The system of Marshallian demands in (5), with full Prices and full budget
variables, was estimated for the three Northern California whalewatching sites (Point
Reyes, Half Moon Bay, and Monterey) via maximum likelihood, using Gauss MAXLIK
Version 4.0.22. Because the data rePresented visitors intercePted at the sites (i.e., those
with Positive quantities), the demand errors are likely to be truncated and this must be
taken account of in estimation. If one writes the latent demand for site i as
x?(p0,M0) = (" - #3)e#!+!#4P0 + "3M0 + %з,
(23)
then a positive quantity x3(p0,M0) is observed when x?(p0,M0) > 0, or when
%3 > - [("3 - #3)e#!+!#4p0 + "3M0].