In this paper, several seasonal unit root tests are analysed in the context of structural breaks at known time and a new break corrected test is suggested. We show that the widely used HEGY test as well as an LM variant thereof are asymptotically robust to seasonal mean shifts of finite magnitude. In finite samples, however, experiments reveal that such tests suffer from severe size distortions...

A time series model with possibly a randomized unit root and a randomized seasonal unit root is considered. Two statistical tests are developed for the null hypothesis of 3xed unit roots against the alternative that the roots are random and 5uctuate about the value of one. The testing problem is addressed via the score test approach. The asymptotic representations of the test statistics in term...

Both seasonal unit roots and periodic variation can be prevalent in data. In the testing of under variation, validity existing methods, such as HEGY test, remains unknown. The behavior augmented test unaugmented is analyzed. It turns out that asymptotic null distributions statistics single at 1 or − when there are identical to no variation. On other hand, any coexistence 1, , i non-standard dif...

Time series quite often show patterns that repeat periodically. Monthly retail sales provide a good example. If the seasonality is very regular, seasonal dummy variables can be used to give, for example, a monthly effect for each month. With this approach, the January effect is assumed to be the same regardless of the year. Seasonal ARMA error terms can be added to make some local modifications...

The objective of this study was to model seasonal behavior of broiler price in Iran that can be used to forecast the monthly broiler prices. In this context, the periodic autoregressive (PAR), the seasonal integrated models, and the Box-Jenkins (SARIMA) models were used as the primary nominates for the forecasting model. It was shown that the PAR (q) model could not be considered as an appropri...

The literature has been notably less definitive in distinguishing between finite sample studies of seasonal stationarity than in seasonal unit root tests. Although the use of seasonal stationarity and unit root tests is advised to determine correctly the most appropriate form of the trend in a seasonal time series, such a use is rarely noted in the relevant studies on this topic. Recently, the ...

In the context of regression-based (quarterly) seasonal unit root tests, we examine the impact of initial conditions (one for each quarter) of the process on test power. We investigate the behaviour of the OLS detrended HEGY seasonal unit root tests of Hylleberg et al. (1990) and the corresponding quasi-differenced (QD) detrended tests of Rodrigues and Taylor (2007), when the initial conditions...