Spurious deterministic seasonality

It is sometimes assumed that the R2 of a regression of a first-order differenced time series on seasonal dummy variables reflects the amount of seasonal fluctuations that can be explained by deterministic variation in the series. In this paper we show that neglecting the presence of seasonal unit roots may yield spuriously high values of this coefficient

Succession of postglacial mud snails (Hydrobiidae) with notes on morphological types of Hydrobia ulvae and larval shells of three species

Postglacial sequence of migration and extinction has been studied in a boring through 10 m deposits in Jutland, Denmark. The main profile contained freshwater and brackish water fauna in the bottom layer. Hydrobia ulvae was first recorded at -9.75 m. Next H. ventrosa was found together with H. ulvae. Then H. neglecta appeared, and all 3 species co-occurred at -8.75 m. At -4.95 m H. ulvae disappeared but H. ventrosa and H. neglecta were still abundant until a depth of -1.90 m. It is concluded that H. ulvae and H. ventrosa quickly colonized the Littorina Sea while H. neglecta may have arrived somewhat later. H. ulvae has the largest larval shell, especially in the Baltic, and H. ventrosa the smallest larval shell of the 3 species. The ecological significance of two markedly different shell forms of H. ulvae is discussed. Postglacial hydrobiids are compared with recent specimens of the 3 species

Testing for seasonal unit roots in heterogeneous panels

This paper uses the approach of Im, Pesaran and Shin (2003) to propose seasonal unit root tests for dynamic heterogeneous panels based on the means of the individuals HEGY test statistics. The standardised t-bar and F-bar statistics are simply averages of the HEGY tests across groups. These statistics converge to standard normal variates