HEGY4: Stata module to compute Hylleberg et al seasonal unit root test
Christopher F. Baum, Richard Sperling · RePEc: Research Papers in Economics · 2001
hegy4 performs the Hylleberg et al. (HEGY) test for seasonal unit roots in a quarterly timeseries. It estimates the four roots of the timeseries representation (1-B^4) x(t) = e(t), where B is the backshift operator, and presents estimates of these roots as Pi(1)..Pi(4). Joint tests for Pi(3)=Pi(4)=0, Pi(2)=Pi(3)=Pi(4)=0 and Pi(1)=Pi(2)=Pi(3)=Pi(4)=0 are calculated (the latter two proposed by Ghysels et al.) The routine will also estimate the model with seasonal trends proposed by Smith and Taylor. This is version 1.0.5 of the routine, which corrects an error in the tabulation of critical values.