Biases in measurement of dynamics of time series from calculation of half- life received more attention lately. In particular, this issue amplifies the controversy surrounding the purchasing power parity doctrine. Cross-sectional and temporal aggregations along with mis-specified models were identified before as sources of this bias. We identified a few other sources of bias, namely, sampling error, wrong approximations, and structural breaks in time series. These sources should receive adequate attention for a sound measure of half-life.