Risk premia and macroeconomic conditions  There is no univocal way to assess whether asset values are high or low relative to economic norms. Popular commentary often focuses on price indices and how they deviate from longterm averages.
But, of course, index levels can vary because of general price inflation, or growth in the real economy, or changes in the size of publicly traded assets relative to the economy. So, it is customary for analysts to scale asset prices in various ways.