Far too much of the Democratic primary has been consumed with determining the boundaries of what is and is not serious. Four former chairs of the Council of Economic Advisers under Presidents Clinton and Obama provided the latest example this week, writing an open letter to castigate a fellow economist, Gerald Friedman of the University of Massachusetts-Amherst.

Friedman conducted a study of how the economy would react over the next ten years if Bernie Sanders’s entire program—free college, universal health care, new infrastructure spending, an expanded Social Security, the works—were adopted. And it included some very optimistic numbers: the creation of 26 million jobs over the next ten years, annual economic growth of 5.3 percent, and a return of the labor force participation rate back to 1999 levels. The Sanders campaign didn’t appear to solicit the Friedman study, but it has been citing it to the media.

The Democratic CEA chairs—Laura D’Andrea Tyson, Christina Romer, Austan Goolsbee, and Alan Krueger—believe these numbers undermine their efforts “to make the Democratic Party the party of evidence-based economic policy.” They add: “These claims undermine the credibility of the progressive economic agenda and make it that much more difficult to challenge the unrealistic claims made by Republican candidates.”

I don’t feel it necessary to defend Friedman, though it’s worth pointing out that his economic growth numbers would simply eliminate the GDP gap that was created by the Great Recession and was never filled in the subsequent years of slow growth—which should be the goal of public policy, however “extreme” it sounds. What I do want to challenge is the idea that there’s one serious, evidence-based way to perform economic forecasting.

The truth is that most economic forecasts that look several years into the future are flawed, almost by definition. This is a sprawling country with countless different economic inputs and knock-on effects that are incredibly difficult to accurately predict with a model. Unexpected exogenous events and misinterpreted implications can make forecasts vary sharply with reality, no matter how carefully they’re constructed. There’s no right or wrong way to divine results from policies, and saying so actually makes you look far less evidence-based than you think. The best example of this comes from the reports of these four CEA chairs themselves.