This neutral rate is not, however, an observable magnitude: there is no statistical release you can consult to find out its value. Nor, of course, are other magnitudes which are common in the lexicon of macroeconomic policy, like ‘full employment’, ‘price stability’, or ‘sustainable growth’.
We can offer a conceptual definition of these terms, but empirical estimates of them always have a margin for error and can never be assumed to be immutable. That does not render the ideas useless; indeed, people expect us to pursue some of them as policy goals.