Percent of "yes"-replies to 22a: "In the last five years, have you signed a petition about an environmental issue?".

In Environment III (2010) - question 22a.
In Environment II (2000) - question 21a.
In Environment I (1993) - question 21a.

A higher score means that more people signed petitions for environmental issues in the 2 years prior to the survey. A lower score means that fewer people signed petitions for environmental issues in the 2 years prior to the survey.