Interestingly, longitudinal data suggests that political polarisation is intensifying, at least in the United States, with the recent US election seeing partisanship reach an all-time high.
One important contributor to this phenomenon is confirmation bias: the tendency to seek or interpret evidence as supporting our pre-existing beliefs, regardless of whether it really does.
Any frequent user of social media is probably aware of the tendency for both sides of politics to view the other as fundamentally immoral and ignorant. There is also research showing that confirmation bias is particularly active when the evidence at hand threatens the validity of our political worldview.
An experiment on bias
To illustrate this phenomenon, Yale University's Dan Kahan and colleagues ran an experiment to see how our political biases influence the way people interpret hard data.
They presented participants with two tables of made-up data about the link between gun control and crime rates. The numbers in both tables were identical; the only difference was the labels were switched. One referred to the efficacy of a fictional skin care cream and the other referred to the effect on crime of carrying handguns (see below).