There are two approaches, labelled “MtM” and “Off”, respectively corresponding to “mark to market” and “off market” (the latter formerly called smoothing).
MtM Assumption The initial discount rate is now always the yield on long-term conventional gilts because I am now excluding index-linked gilts. While simplistic, it is not only simple but also not that far away from what broadly tends to have been assumed. This can either be taken as it is or increased by 1% pa.
Off Assumption For equities and bonds, the expected return is estimated as a multiple of the initial yield. Using random numbers and past experience, the multiples have been set separately for each of the 4 experiences (see below). Were I still including ILGs, I would still have chosen “yield + expected long-term inflation + 1%” (taken from ukrpi.com). For 2022, I have looked at the results obtained if we further multiply these numbers by 80% OR 100% OR 120%.
To illustrate further, for the blend experience, the “Off” expected equity return wou;d be assessed as the random equity yield multiplied by 1.82 OR 2.27 OR 2.72.
Although these are based upon past actual experience means, we don’t actually need to use scalars. However, I have done so because I thought that the random numbers were excessively volatile. The historical results are charted here.