In a few days, Americans will choose a president. Opinion polling suggests that voters favour former Vice President Joe Biden when it comes to social policy, foreign policy, the environment, and managing the pandemic, not to mention personal character. But until recently, some polls indicated that on the economy, voters favoured President Donald Trump.

The general impression that the US economy does better under Republicans than Democrats is long-standing. But the facts do not support it.

In the 16 complete presidential terms since World War II, from Harry Truman through Barack Obama, annual GDP growt...