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...

The contribution of this paper is three-fold. Firstly, a characterisation theorem of the sub-hypotheses comprising the seasonal unit root hypothesis is presented which provides a precise formulation of the alternative hypotheses against which regression-based seasonal unit root tests test. Secondly, it proposes regressionbased tests for the seasonal unit root hypothesis which allow a general se...

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...

agriculture as one of the major economic sectors of iran, has an important role in gross domestic production by providing about 14% of gdp. this study attempts to forecast the value of the agriculture gdp using periodic autoregressive model (par), as the new seasonal time series techniques. to address this aim, the quarterly data were collected from march 1988 to july 1989. the collected data w...

A lot of time series analysis in economics and nance is to determine whether a unit root and/or seasonal unit root is present in the data. These tests are usually based on unit root tests orginally developed by Dickey & Fuller(1981). Testing for the presence of a seasonal root has been considered by Dickey, Hasza & Fuller (1984). Li(1991) considered tests for the existence of a seasonal and a r...

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 ...

Linear filters used in seasonal adjustment (model-based or from the X-11 method) contain unit root factors in the form of differencing operators and seasonal summation operators. The extent to which the various filters (seasonal, seasonal adjustment, trend, and irregular) contain these unit root factors determines whether the filters reproduce or annihilate (i) fixed seasonal effects, and (ii) ...

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...