American state legislators are far more ethnocentric than Canadian MPs

Evidence

It may be invalid to compare national lawmakers with state legislators. Still, a lot (43) of the elected American officials scored higher than the 50 posted by the most ethnocentric Canadian lawmaker. — Bob Altemeyer, The Authoritarian Specter, 3519

Categorization

• QUESTION: Why would American state legislators be so much more ethnocentric than Canadian national lawmakers? Is it national culture, self-selection into office, or measurement issues?