Hong Kong has stood alone for 25 years atop the Heritage Foundation’s annual Index of Economic Freedom. The index scores 180 economies around the world in 12 categories of economic freedom related to the rule of law, regulatory efficiency, government size and the openness of markets. It averages those scores to get an overall economic freedom score on a 100-point scale. Hong Kong’s lead over perennial second-place finisher Singapore has been as wide as 4 points, but in recent years Hong Kong’s lead has dwindled to less than a point.

The...