On Periodic Correlations Between Estimated Seasonal and Nonseasonal Components in German and U.S. Unemployment
检验德国和美国官方季度失业数据中季节与非季节成分的正交性假设，发现非周期相关不拒绝该假设，但基于季节变化的周期相关分析表明正交性被违反，且未调整数据可用带单位根的周期自回归模型描述。
We examine the orthogonality assumption of seasonal and nonseasonal components for official quarterly unemployment figures in Germany and the United States. Although nonperiodic correlations do not seem to reject the orthogonality assumption, a periodic analysis based on correlation functions that vary with the seasons indicates the violation of orthogonality. We find that the unadjusted data can be described by periodic autoregressive models with a unit root. In simulations we replicate the empirical findings for the German data, where we use these simple models to generate artificial samples. Multiplicative seasonal adjustment leads to large periodic correlations. Additive adjustment leads to smaller ones.