An Update on Priorities and Expenditures under the Endangered Species Act
重新评估1993-1996年间联邦保护241种濒危脊椎动物的支出决策，发现年度变化因素（如濒危等级、经济冲突）对支出无显著影响，暗示时间不变特征（如物种魅力）才是关键。
<i>This paper reevaluates federal allocation decisions to protect 241 endangered vertebrates between 1993–1996. We control for the time invariant species characteristics to address species heterogeneity bias. The results suggest that yearly variation in variables like endangerment rankings and economic conflict now have no significant effect on the expenditures. This finding implies either these factors did not vary enough during the time frame or their impact has been biased upward in non-panel data exercises. This suggests any combination of time invariant factors, from charisma to the underlying ecosystem and historical uses as game species, could explain federal outlays for species protection.</i>