How cognitive biases affect our interpretation of political messages

British readers of the BMJ will soon get to vote on the competing visions of the political parties at the general election. Although the mainstream parties each claim the middle ground, there are important differences in how they will approach the economic challenges that lie ahead, with potentially major implications for health and health care. How fast and how deep should cuts in public spending be? Are targets a good or a bad thing? What is the appropriate role of private healthcare providers?

Voters must decide which of the different answers they agree with, yet—as seen in recent disputes between leading economists about how to tackle the government deficit—it is possible for two well informed groups of people faced with the same evidence to reach completely different conclusions about what should be done. How do voters interpret such complex information and what influences them?

There is considerable evidence that people presented with balanced arguments place weight on those they already agree with,1 exhibiting what is termed confirmation bias.2 …