The first sentence of the introduction clarifies the definition of "political tolerance", which seems to be a term of art; "Citizen support for the rights and liberties of even those political groups that they dislike, commonly termed political tolerance, is an important element of liberal democracy." So what is being measured is support for the civil liberties of political groups that are disliked by the respondent. Survey respondents were given a list of groups and asked to rate, from -4 to 4, a. how much they liked that group, and b. how much they would protect that group's rights.