Forecasting Rolling Year Indices using Month to Month Annual Basket Indices

For each of the series, Lowe, Young and Geometric Laspeyres, a seasonal adjustment factor (SAF) is defined, as the centered rolling year index P_CRY divided by P_LO, P_Y and P_GL, respectively for the first 12 observations. Now for each of the three series, repeat these 12 seasonal adjustment factors for the remaining observations. These operations will create 3 SAF series for all the observations (label them SAF_LO, SAF_Y and SAF_GL, respectively).

Finally, define seasonally adjusted Lowe, Young and Geometric Laspeyres indices by multiplying each unadjusted index by the appropriate seasonal adjustment factor.

A seasonally adjusted version of the Rothwell index presented in the paper may also be defined in the same way.