Discussion of Results
Table 2 and 3 report the estimated slope parameters of List 1 through 4 for 1997 and 2002,
respectively. The intercept dummies in equation (12), i.e., (α0,δ0) , are not presented due to
space limitations. Results in table 2 and 3 relate the four representations of regulatory
congruence to dissimilarities in ecosystem, agronomy, and lobby strength across states. So,
coefficients are interpreted as effects of dissimilarities between a base state and a comparator
state on regulatory congruence between the two states. Since fewer states have NXW lists with
varying degree of control, the following discussion weighs more on results from NXWS list.
Ecological Dissimilarities and Regulatory Congruence: In table 2, we first present the results on
ecological variables, each of which had two coefficients corresponding to the sign or strength of
dissimilarity between the base and comparator states. Consistent with the hypothesis in figure 2,
we obtained significant negative slope coefficients for most temperature and precipitation
indexes when the strength of dissimilarity is biased toward the comparator state. Similarly, when
the dissimilarity index favored the base state, most coefficients on temperature and precipitation
indexes have the expected positive sign with statistical significance. There are a few exceptions,
mostly in List 4. With regard to the 2002 results in table 3, we find that the effects of ecological
variables, proxied by temperature and precipitation dissimilarities, are similar to those in table 2
(1997). For each of the two years, of the 32 coefficients representing temperature and
precipitation dissimilarities, only 4 have the unexpected sign with statistical significance. In
general, the above results suggest that the relationship between ecological characteristics and
noxious weed regulatory differences is best illustrated by figure 2. That is, divergence in
ecological characteristics, represented by average and variance of temperature and precipitation,
is an important determinant of NXWS and NXW regulatory congruence across states.
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