Complex constituencies: intense environmentalists and representation

The role of environmental subconstituencies in determining the voting behaviour of members of the US Congress is assessed. Using ordinary least squares and symmetrically censored least squares (a method especially appropriate for bimodal data), the impact of environmentally-concerned constituents, as measured by original data on environmental group membership, on congressional voting is quantified. In general, members of the US Congress vote more pro-environmental when they have more environmental group members in their districts, which may be representation or factionalism at work. Surprisingly, even though members of environmental groups are a traditionally Democratic constituency in the United States, both Democrats and Republicans are responsive.