Supplementary materials to: The changing association between political ideology and closedmindedness: Left and right have become more alike

Evidence suggests that politically right-leaning individuals are more likely to be closed-minded. Whether this association is inherent or subject to change has been the subject of debate, yet has not been formally tested. Through a meta-analysis, we find evidence of a changing association between conservatism and facets of closed-mindedness in the U.S. and international context using 341 unique samples, over 200,000 participants, and 920 estimates over 71 years. In the U.S., data ranging from 1948 to 2019 revealed a linear decline in the association between social conservatism (SC) and closed-mindedness, though economic conservatism (EC) did not vary in its association with closed-mindedness over time. Internationally across 18 countries, excluding the U.S., we observed a curvilinear decline in the association between SC and closed-mindedness over that same time, but no change in ECs association. We also tested variation over time for attitudinal measures of conservatism ranging between 1987 to 2018. In the U.S., we observed a linear increase in the association between right-wing authoritarianism (RWA) and closed-mindedness, with a similar linear increase in the association between social dominance orientation (SDO) and closed-mindedness. Internationally, there was a curvilinear increase in the association between RWA and closed-mindedness, but no change in the association with SDO. We discuss the changes to the political landscape that might explain our findings.