Source: Laubach and Williams (2003), “Measuring the Natural Rate of Interest,” Review of Economics and Statistics, Holston, Laubach, and Williams (2017), “Measuring the Natural Rate of Interest: International Trends and Determinants,” Journal of International Economics, and Pedersen (2015), "The Danish natural real rate of interest and secular stagnation", Danmarks Nationalbank Working Papers.
That general trajectory, as opposed to one point on it, was given some weight. More generally, economic forecasting is difficult and imprecise. In practice, it can sometimes be hard for the forecasters to make a confident call that higher or lower inflation is on the cards until it is imminent or even under way. Similar problems characterise forecasts for other variables.