To assess interparty completion in democratic politics, Dalton (2008) constructed the “party polarization index” based on a left-right ideology. The partisan divide between the pan-Blue and pan-Green camps in Taiwan has been sharp and acute since the 1990s.  This observed reality contradicts the stable and modest prediction based on Dalton’s index. To explain the difference, it is hypothesized that public opinion in Taiwan rests not on a left-right ideological continuum but on the issue of independence versus unification. This study utilizes cognitive interviews and survey data conducted in Taiwan to examine its citizens’ perceptions of left-right ideology in an attempt to adjust Dalton’s party polarization index.

This research shows that most of Taiwan’s citizens are unfamiliar with, and sometimes misunderstand, the meaning of left-right ideology. The majority of the respondents cannot place themselves or identify the major parties’ positions on a left-right ideological continuum. The result indicates that Dalton’s party polarization index is inappropriate to examine Taiwan’s interparty competition due to the validity issue in measurement. By replacing the indicator of left-right ideology with that of the respondents’ positions on the unification versus independence issue, this study shows that Dalton’s index can better assess interparty competition in Taiwan. The implication of the findings from this study is that the index construction needs to adapt to different political contexts.