A decade and a half after the devastating 9/11 terrorist attack, Randall Forsyth of Barron’s says the American economy still feels the impact.

Other economists have tried to discern how, and how much, the war on terrorism has exerted a drag on economic growth. Among them, Todd Sandler and Walter Enders, economists at the University of Texas at Dallas and the University of Alabama, respectively, observe that the direct costs of attacks pale against the far greater indirect costs, which include forgone output, increased security outlays, and a high risk premium, resulting in lower stock prices.

Even more to the point, they wrote in their book The Political Economy of Terrorism: “In response to a sustained level of terrorism, governments increase their homeland security expenditures. Such expenditures tend to crowd out private capital formation in such a way that the overall level of growth is reduced. Because growth effects are cumulative, slight changes in growth rates can have a substantial effect on the long-term standard of living.”

This may be an underappreciated aspect of the ongoing lack of productivity growth at the core of the populist discontent with stagnant incomes. The impact of increased antiterrorism efforts can only be guessed, but as Einstein reportedly said, not everything that counts can be counted, and not everything that can be counted counts. Some of the measures seem to be a literal waste of time and money, such as the screening procedures at airports. Conversely, we will never know how many attacks have been thwarted and lives have been saved as a result of increased intelligence since 9/11.

Freedom isn’t free, and neither does it come cheaply, both in terms of direct outlays and their effect on the greater economy. We have come a long way in the past 15 years, but the heavy toll of that fateful day remains.