The Discussion Papers series presents results from ongoing research projects and other research and analysis by SSB staff, intended for international journals or books. The views and conclusions in this document are those of the author(s). 

First, we propose a robust univariate filter that accounts for extreme observations — such as the COVID–19 pandemic — by treating them as additive outliers. Second, we develop a multivariate HP filter that incorporates time–varying, import–adjusted budget shares of GDP sub–components. This adaptive weighting minimizes cyclical variance and yields a more stable trend estimate. Applying the framework to U.S. data, we find that private investment is the dominant source of cyclical fluctuations, while government expenditure exhibits a persistent counter–cyclical pattern. The proposed approach enhances real–time policy analysis by reducing endpoint bias and improving the identification of cyclical dynamics.