Like other filters, one limitation of the HP filter is that the estimated trend is more sensitive to transitory shocks or short-term fluctuations at the beginning and at the end of the sample period. This results in a sub-optimal performance of the HP filter at the endpoints of the series (Baxter and King, 1999). In view of this property, trend series are not published for the first and last two years for which data on actual labour productivity growth are available.
An important aspect of the HP filter is the value of the smoothing parameter λ. While for quarterly data a value of λ=1600 has typically been assumed (as recommended by Hodrick and Prescott, 1997), there is less agreement on the value which should be used when the filter is applied to other frequencies (e.g. annual, monthly). The value of λ selected here is 54.12 and has been determined by calibrating the Hodrick-Prescott filter in such a way that cycles shorter than 9.5 years are attenuated by 90% or more (Chapter 8. ).
Official data for Germany after unification are available only from 1991 onwards. Estimates for Germany as a whole back to 1970 have been derived by applying the relevant growth rates for West Germany to 1991 data.