Always compare yields to inflation

Note \(Y^m_t\) the yield of the bond of maturity \(m\) bought at time \(t\), \(P_{t-1}\) the CPI at previous time, \(P_t\) the CPI at current time and compute:

\begin{equation} Y^m_{t} - \frac{P_{t}-P_{t-1}}{P_{t-1}} \end{equation}

Note: This is one very narrow definition of inflation, yet we use because everyone does to make decisions. We should probably use another name.