Often when analysing financial markets, we want to know the statistical distribution of some financial market prices, yields or returns. But the ‘true’ distribution is unknown and unknowable. So we estimate the distribution, based on what we’ve observed in the past. In financial markets, adding one data point can make a huge difference. Sharp moves in Italian bond yields in May 2018 are case in point – in this blog I show how a single day’s trading drastically alters the estimated distribution of returns. This is important to keep in mind when modelling financial market returns, e.g. for risk management purposes or financial stability monitoring.